[heyitsnick]

"I met a man on the street, he said he had two children. I asked him, is at least one of them a boy? He said yes. What's the probability both of them are boys?"

This removes the whole ambiguity of why he would assert "at least one of them is a boy," but still makes the question a bit tricky/counter-intuitive, which is useful for teaching the quirks of probability.