It is indeed peculiar. I've hypothesized that such people don't think about what they are saying, and being asked to thin about what they are saying makes them aware of the fact that what they are saying is illogical, irrational, or selfish/silly.

So, I THINK what happens is that in being asked to clarify, they examine their own thoughts, and realize that their own thoughts make no sense or represent something negative about their personality. They don't like this feeling, so they lash out at the person asking them as if the person asking them is doing something aggressive.

Just my hypothesis!