2.10. A man was brought before a tribal chief, who asked him a question. If he had known the answer, he probably would have died. He didn't, and lived. (MWD original)
2.10 answer: The native chief asked him, "What is the third baseman's name in the Abbot and Costello routine 'Who's on First'?" The man, who had no idea, said "I don't know," the correct answer. However, he was a major smartass, so if he had known the answer he would have pointed out that What was the second baseman's name. The chief, being quite humorless, would have executed him on the spot. This is fairly silly, but I like it too much to remove it from the list.
2.10 variant answer: The question was, "What does the tattoo on my daughter's tush say?" or any other question whose answer reveals that you know more than you should. Of course, for this sort of question one can lie and say one doesn't know even if one does. (FF)