To be fair, almost everyone hates it when you show them they are wrong. Especially in the setting where they are supposed to be judging you, remember? And even in normal settings it pays to think about how some critique will be received by the other side. It's a slippery slope in the interview... For me it would raise red flags if the flaw was pointed out in an inappropriate manner. After all, this is the person who would be involved in code reviews where sensitivity to other people's feelings (and egos) is very important.