One question martial artists hear all the time is: "Do you think you can beat them up?" followed by the asker pointing to the biggest, baddest-looking person in the room.
There's also, "Could you break that tree/board/desk/etc. with a chop?"
And of course, there's the question that commonly follows the demonstration of a self-defense technique: "But what if…. (insert some random occurrence that's less likely to happen than winning the lottery while being struck by lightning) happens?"
(The answers usually are, in order, "Why would I," "Why would I," and, "Well, then, I guess you're toast – but I think the odds of you being attacked by a rollerblading BJJ master who's wielding double shotguns are comfortable low.")