You've almost certainly heard it, or been party to it on one side or another. It's the one that starts "What are you eating under there?"
I recall the first time I was on the poor end of that one, but not because I was made a fool of. Rather, because the frustrated reaction was memorable. It went something like, but not exactly like, this:
"What are you eating under there?"
"I'm not eating anything, can't you see that?"
"Well, if you were eating, what are you eating under there?"
"Under what?"
"You're supposed to say 'under where?'!"
"But that doesn't make any sense."
"Yes it does. Then it sounds like 'underwear.' That's the joke."
"It's not a very good one."
An odd bit to recall, but it is one of the earliest pieces of actual conversation that I can recall with anything even approaching accuracy. Strange what is still remembered so many years later. I'd like to claim it was superior reasoning that came to my aid, but more likely it was dumb luck and poor timing on the joker's part.