"When was the last time you prevaricated?"
Semantically it's a sensible question, and a computer would probably try and answer it, but a human being would just say - "Awee... c'mon.. how the hell would I know?"
Anything with that pattern, ie. linguistically, semantically, and culturally a sensible question, but something which no real person would ask, or answer. (This can be done, without going into deeply personal areas - in fact, the computer might be programmed to handle those with "that's private").