I've actually gotten the opportunity to use one of these. In eighth grade, I was asked, "What's long and hard and full of seamen?" I didn't answer, and was informed of the proper response ("A submarine!") Some time later, the kid who asked me pointed me out to his friends and told them that I hadn't been able to answer his question, and having thought about it in the interval, I said to him, "I was just thinking that whatever it was, it wasn't yours." I consider that the crowning moment of my middle school career.

I was in a history class my freshman year of college, and a classmate accidentally called Senator [=McCarthy=] "[=McCartney=]." The professor promptly corrected him, and about a minute too late, I realized I had missed the golden opportunity to interject that the difference was "this one ''hated'' Lenin!"

Happens so frequently that this troper occasionally times himself until a snappy comeback springs to mind. He averages something around two minutes.

During this troper's school experience, several the girls in middle school science class once discussed the flaws of the male gender, and came to the conclusion that "Girls rule and boys drool." Which they repeated several times. It wasn't until I was out of school for a year, and had lost contact with everyone I'd gone to school with, that this trope kicked in. I should have said, "Maybe if certain girls didn't give us so much to drool over..." Of course, that would have sounded disturbing coming from a middle-schooler... - Classified

This is what inspired me to start learning witty humour.