Snappy Answer

A college teacher reminds her class of tomorrow's final exam. "Now class, I won't tolerate any excuses for you not being here tomorrow. I might consider a nuclear attack or a serious personal injury or illness, or a death in your immediate family but that's it. No other excuses whatsoever!"

A smart-ass guy in the back of the room raises his hand and asks, "What would you say if tomorrow I said I was suffering from complete and utter sexual exhaustion?" The entire class does its best to stifle their laughter and snickering. 

When silence is restored, the teacher smiles sympathetically at the student, shakes her head, and sweetly says, "Well, I guess you'd have to write the exam with your other hand."