A brain like a BB in a boxcar.
A couple of bricks short of a hod.
A couple of dilithium crystals short of a warp core.
A couple of knights short of a Crusade.
A couple of togas short of an orgy.
A couple of volts below threshold.
A couplet short of a sonnet.
A day late and a dollar short.
A few beers short of a six-pack.
A few birds shy of a flock.
A few bits short of a byte.
A few bits shy of a word.
A few bricks shy of a load.
A few cans short of a six pack, six short.
A few clowns short of a circus.
A few clues shy of a solution.
A few ears short of a bushel.
A few eggs short of a dozen.
A few feet short of the runway.
A few fish short of a string.
A few guppies short of an aquarium.
A few inches short of a foot / yard.
A few kernels short of an ear.
A few lanes short of a highway.
A few lines short of a program.
A few links shy of a chain.
A few open splices.
A few peas short of a pod / casserole.
A few pickles short of a jar.
A few pixels short of an image.
A few puppies short of a pet shop.
A few rungs short of a ladder.
A few sandwiches / apples / ants short of a picnic.
A few screams short of an orgasm.
A few screws loose.
A few snowballs short of an avalanche.
A few spoons short of a full set.
A few straws shy of a bale.
A few tacos short of a fiesta platter.
A few tiles missing from his Space Shuttle.
A few tomatoes short of a thick sauce.
A few yards short of the hole.
A flower short of an arrangement.
A goose short of a gaggle.
A hamburger / a few French fries short of a Happy Meal.
A handle short of a suitcase.
A hump short of a camel.
A lap behind the field.
A little light in his loafers.
A looney tune.
A mind like wet tennis shoes: Makes squishy noises when running.
A pane short of a window.
A photographic memory, but the lens cover is glued on.
A pickle short of a barrel.
A quart low.
A room temperature IQ.
A screw loose.
A strawberry short of a quart.
A teabag short of a pot.
A victim of retroactive birth control.
A violin minus the bow.
A walking argument for birth control.
A wind-up clock without a key.
About a half a bubble off plumb.
About as sharp as a sack of wet leather / a bowling ball / a bowl of Jell-O.
About as smart as bait.
About fifteen cents short.
About three cents short of a dollar.
Ain't wrapped too tight.
Air between the ears.
All booster - no payload.
All booster and no shuttle.
All crown - no filling.
All foam. no beer.
All hammer, no nail.
All his eggs in the same basket.
All his marbles in one bag.
All lime and salt, no tequila.
All missile, no warhead.
All plow and no tractor.
All the lights don't shine in his marquee.
All the sex appeal of a wet paper bag.
All wax and no wick.
Almost as smart as a finch.
Always in the right place, but at the wrong time.
Always sharpening his sleeping skills.
An early example of the Peter Principle.
An ego like a black hole.
An experiment in Artificial Stupidity.
An inch short and a stroke early.
An intellect rivaled only by garden tools.
Answers the door when the phone rings.
Antenna doesn't pick up all the channels.
Any slower and he'd be in reverse. -- Gignac
As bright as a nightlight / small appliance bulb / tulip bulb.
As thick as two short planks.
Attention span of an overripe grapefruit.
Attic's a little dusty.
Back burners not fully operating.
Bats have flown the belfry, and now he's all alone.
Bats in the belfry.
Batteries not included.
Been playing in the pharmacy section again.
Been playing with his wand too much.
Been short on oxygen one time too many.
Blender doesn't go past "mix".
Blocked one too many hockey pucks / soccer balls / punches.
Body by Fisher - Brains by Mattel.
Born a day late and like that ever since.
Born during low tide in the gene pool.
Both oars in the water, but on the same side of the boat!
Brain on cruise control.
Brain speed inversely proportional to mouth speed.
Brains of a house plant.
Bright as a Zippo lighter without a flint.
Bright as Alaska in December.
Caboose seems to be pulling the engine.
Cackles a lot, but I ain't seen no eggs yet.
Calling him a pea brain would be an undeserved compliment.
Can be outwitted by a jar of Marshmallow Fluff.
Can carry on conversations with bushes.
Can easily be confused with facts.
Can't find his ass with two hands and a periscope.
Car's only got three wheels, and one's going flat.
Cauliflower / Cheezwiz for brains.
Cheats when filling out opinion polls.
Clutch is slipping.
Could get lost in a broom closet.
Couldn't find his way through a maze even if the rats helped him.
Couldn't hit sand if he fell off a camel.
Couldn't pick the winner of a one-horse race.
Couldn't spell "cat" if you spotted him on the "C" and the "A".
Couldn't write dialog for a porno flick.
Crazy as all get out / a loon.
Cursor's flashing but there's no response.
Deaf, dumb, and blonde.
Deck has no face cards.
Diagonally parked in a parallel universe.
Dialing thumb must be broken.
Dock doesn't quite reach the water.
Does aerobics... in his head.
Doesn’t have all nine players on the diamond.
Doesn't have all his dogs barking.
Doesn't have all of his groceries in the same bag.
Doesn't have all the dots on his dice.
Doesn't have both chop sticks in the chop suey.
Doesn't have both oars in the water.
Doesn't have both oars in the water -- can't even find the damn boat.
Doesn't have elastic in both of his socks.
Doesn't have his belt through all the loops.
Doesn't have the sense God gave an animal cracker.
Doesn't just know nothing; doesn't even suspect much.
Doesn't know if he's afoot or on horseback.
Doesn't know which side of the toast the butter is on.
Downhill skiing in Iowa.
Dr. Kevorkian got her from the neck up.
Driving with two wheels in the sand.
Dumb as asphalt / dirt / a stump / a box of rocks / a sack of hammers.
Dumber than a chicken / box of hair / a red brick / rocks.
Dumber than owl droppings.
During evolution his ancestors were in the control group.
Easier to count the bricks left than the bricks missing.
Eating with only one chopstick.
Echoes between the ears.
Elevator doesn't go all the way to the top floor.
Elevator doesn't make it to the penthouse.
Elevator doesn't stop at every floor.
Elevator goes all the way to the top but the door doesn't open.
Elevator is stuck between floors.
Encyclopedia’s missing some volumes.
Engine is running, but no one is behind the wheel.
Enough sawdust between the ears to bed an elephant.
Evidence for the theory of a missing link.
Flying / landing on one engine.
Forgot to pay his brain bill.
Found his marbles, but is playing jacks with them.
Four cents short of a nickel.
Full throttle, dry tank.
Gasoline engine, diesel fuel.
Gates are down, the lights are flashing, but the train isn't coming.
Gavel doesn't quite hit the bench.
Gets her mail at an unknown zip code.
Gets his orders from another planet.
Gives a lot of bull for somebody what ain't got no cattle.
Goalie for the dart team.
God might still use him for miracle practice.
God's favorite target for lightning strikes.
Got a dozen eggs but some are cracked.
Got a life, but wasn't sure what to do with it.
Got into the gene pool while the lifeguard wasn't watching.
Half a brick short of a full load.
Half a bubble off plumb. --Attributed to Mark Twain
Half a quart low.
Hard to distinguish from the tail end of a horse.
Has a leak in his ceiling.
Has a pulse, but that's about all.
Has all her bricks, but no cement holding them together.
Has all the brains God gave a duck's ass.
Has six beers, but lacks the little plastic thing to hold them together.
Has the brains of a dog’s ass.
Has the intellectual capacity of an Allen wrench.
Has the memory of a goldfish.
Has two brains. One is lost and the other is out looking for it.
Hasn't enough sense to pound salt into a rat hole.
Hasn't got all his china in the cupboard.
Hasn't got enough sense to come in out of the rain.
Hasn't got the brains God gave a cat.
Having a party in his head, but no one else is invited.
Head whistles in a cross wind.
Hears everything that a dog can.
He's got his motor running but the gearshift is still in park.
His drill doesn't have a full set of bits.
His jogging trail doesn’t go all the way around the lake.
If brains were bird droppings, he'd have a clean cage.
If brains were dynamite he couldn't blow his hat off / his nose!
If brains were popularity, she’d be the IRS.
If brains were taxed, he'd get a rebate.
If he had another brain cell, it'd be lonely.
If he had brains, he'd take them out and play with them.
If he were any more stupid, he would have to be watered twice a week.
If he were any smarter, you could teach him to fetch.
If his IQ were 2 points higher he would be a rock.
If she were any dumber, she'd be a green plant.
If stupidity were a crime, he'd be #1 on the Most Wanted list.
If stupidity were beauty, her face could launch a million ships.
If the government ever declared war on stupidity, he'd get nuked.
If there were a merciful God he'd be dead by now.
If they made hats the size of his brain he would be wearing a peanut shell.
Immune to caffeine and all other stimulants.
Impervious to brain damage.
In the shopping mall of the mind, he's in the toy department.
Infinite space between her ears.
Inspired the slogan, "A mind is a terrible thing to waste."
IQ lower than a snake's belly in a wagon-rut.
IQ of a salad bar / an ice cube / three below houseplant.
It would be easier to count the bricks left than the bricks missing!
Knitting with only one needle.
Knows Atlanta like the back of her hand, but she’s in Chicago.
Lamborghini chassis, moped engine.
Left the store without all of his groceries.
Library is well stocked - with Dr. Seuss books.
Life by Norman Rockwell, screenplay by Stephen King.
Light not burning too bright.
Lightbulb over his head is burned out.
Lights are on but nobody's home.
Like a one-armed man climbing a rope.
Little red choo-choo done jumped the track.
Lives in the same world, but a different universe.
Living proof of evolution.
Living proof that nature does not abhor a vacuum.
Long on dry wall, short on studs.
Looking for a nickel in the corner of a circular room.
Loony as a jay bird.
Lost his trolleys.
Low on thinking gas.
Marching to a different kettle of fish.
Mental agility of a soap dish.
Mentally qualified for handicapped parking.
Mercifully free of the ravages of intelligence.
Mind is on vacation but his mouth is working overtime.
Mind like a sieve.
Mind like a steel trap - anything entering gets crushed and mangled.
Mind like a steel trap -- full of mice.
Mind like a steel trap -- rusty and stuck closed.
Mind like a steel trap -- things wander in and get mangled.
Mind wandered and never came back.
Missing a few buttons on his remote control.
Missing a few catalog cards / gears / marbles.
Missing a layer of insulation in his attic.
Missing all of the face cards.
Mouth is in gear, brain is in neutral.
Moves his lips to pretend he's reading.
Music by Mozart, choreography by Beavis & Butthead.
Needs another brain to make half-wit.
Needs both hands to wipe his behind.
Nice house, but nobody home / not much furniture.
No coins in the old fountain.
No filter in the coffee maker.
No grain in the silo.
No hands on the rudder / yoke.
No hay in the loft.
No one at the throttle.
No wind in her mind's windmills.
Not digging in the same ditch with the rest of us!
Not done evolving yet.
Not enough brain cells for the Prozac to be effective.
Not enough brains to get anywhere near the gutter.
Not enough sense to come in out of the rain.
Not firing on all four / six / eight cylinders.
Not firing on all thrusters.
Not much to show for four billion years of evolution.
Not only a few brick short, but is missing someone else's bricks as well.
Not only rude, but ugly too.
Not quite human any longer.
Not running on full thrusters.
Not the brightest light on the Christmas tree.
Not the fastest car in the lot.
Not the quickest bunny in the forest.
Not the same since they took him off his medication.
Not the sharpest crayon in the box.
Not the sharpest knife in the drawer.
Not too tightly wrapped.
Not worth pissin' on.
Nothing between the stethoscopes.
Nutty as a fruitcake.
Off his rocker.
Oil doesn't reach his dipstick
On permanent leave of absence from his senses.
On the batting end of a no-hitter.
One banana short of a fruit-salad.
One board short of a porch.
One boot stuck in the sand.
One brick shy of a load.
One drop short of an empty bladder.
One fang short of a vampire.
One Froot Loop shy of a full bowl.
One fruit short of a basket.
One horseman short of an apocalypse.
One hot pepper short of an enchilada.
One live brain cell away from being a talking monkey.
One sentence short of a paragraph.
One shingle shy a roof.
One shingle shy of a roof, and the water's getting in.
One ship short of a full fleet.
One snowflake short of a ski slope.
One song short of a musical.
One step short of the attic.
One tree short of a hammock.
Only got one oar in the water.
Only hitting on 7 cylinders.
Only operating at about half a watt.
Only playing with 51 cards.
Only playing with the jokers.
Ought to have a warning label on his forehead.
Out in left field with a catcher's mitt on.
Outlet isn't grounded.
Over the rainbow.
Overdue for reincarnation.
Paddling with one oar.
Paralyzed from the neck up.
Parked his head and forgot where he left it.
Pedaling real fast, but not getting anywhere.
People around her are at risk of second hand idiocy.
Perfect face for Halloween.
Permanently out to lunch.
Permanently rotated 90 degrees from the rest of us.
Personality of a snail on Valium.
Playing baseball with a rubber bat.
Playing hockey with a warped puck.
Plays solitaire... for cash.
Porch light is on, but there's nobody home.
Proof God has a sense of humor.
Puzzle is missing a few pieces.
Quick as a corpse.
Reading off an empty disk.
Receiver is off the hook.
Renewable energy source for hot air balloons.
Reset line is glitching.
Result of a first cousin marriage.
Riding a tippy canoe.
Room for rent, unfurnished.
Room temperature IQ.
Room temperature IQ - in Centigrade.
Running on empty.
Runs squares around the competition.
Rusty springs in the mousetrap.
Sailboat fuel for brains.
Several nuts over fruitcake minimum.
Several nuts short of a full pouch.
Sharp as a marble / bowling ball / beachball.
She can piss standing up, but not much else.
She only packed half a sandwich.
Short a few cards.
Should be the poster child for family planning.
Should have kept his helmet on while riding / playing.
Signs on both ears saying 'Space for Rent.'
Sitting in the right pew, but the wrong church.
Six bricks short of a full load.
Six shy of a dozen.
Skating on the wrong side of the ice.
Skylight leaks a little.
Slept too close to his radium-dial watch.
Sloppy as a soup sandwich.
Slow as molasses in January.
Slow out of the gate.
Smart as a politician / lawyer is honest.
Smart as bait.
Smarter than the average bear.
Smoke doesn't make it to the top of his chimney.
So boring, his dreams have Muzak.
So dim, his psychic carries a flashlight.
So dumb, blondes tell jokes about him.
So dumb, he faxes face up.
So dumb, his dog teaches him tricks.
So far gone, hard drugs push him closer to normal.
So fat, people climb over him rather than go around.
So slow, he has to speed up to stop.
So slow, we drive stakes in the ground to measure his progress.
So stupid, mind readers charge her half price.
Soft as baby shit.
Soft as silly putty.
Solid concrete from the eyebrows backwards.
Some Assembly Required.
Some bugs in his software.
Some drink from the fountain of knowledge, but he just gargled.
Some M&M's missing from her bowl.
Some pages missing.
Somebody lend her a quarter to buy a clue.
Someone blew out his pilot light.
Strong like bull, smart like streetcar.
Stumped by anything childproof.
Subtle as a well-thrown brick.
Suffers from Clue Deficit Disorder.
Switch is on, but no one's receiving.
Takes her 1.5 hours to watch "60 Minutes".
Talks to plants on their own level.
The carnival has closed.
The cheese has slid off his cracker.
The computer's on but there's no prompt.
The crowd’s cheering but there’s no team on the field.
The going got weird, and he turned pro.
The space between his ears powers vacuum pumps.
The wheel's spinning but the hamster's dead.
There's a leak in his ceiling.
Thick as a brick.
Three chickens short of a hen house
Three wheels short of a Honda.
Too many birds on her antenna.
Too many jokers and not enough aces in his deck.
Too much yardage between the goal posts.
Took the little bus to school.
Toys in the attic.
Traveling without a passport.
Trying out for the javelin retrieval team.
Two bits shy of a word.
Two catchers and three basemen short of a World Series.
Two clowns short of a circus.
Two saucers short of a tea-service.
Two sheep short of a sweater.
Two socks short of a pair.
Types 120 words a minute but her keyboard isn't plugged in.
Ugly as a warthog and half as smart.
Understands English as well as any parrot.
Useful as a balsa wood anchor.
Useful as a chocolate frying pan.
Useful as a concrete canoe.
Useful as a glass machete.
Useful as a kick stand on a horse.
Useful as a one-legged man in an ass-kicking contest.
Useful as an ashtray on a motorcycle.
Useful as tits on a bull / boar-hog.
Useful as tits on a tomcat.
Uses his head to keep the rain out of his neck.
Uses thumbtacks to post notes -- on his refrigerator.
Uses two hands to eat with chopsticks.
Vacancy on the top floor.
Was hiding behind the door when they passed out brains.
Was napping in the nut pile the day that God was cracking nuts.
Welcome light on, but no one home.
Working with an unformatted disk.