The uptight man

Someone just told me about a guy (I have to keep it vague lest they find out) who will over-analyze someone's speech. So for instance, if someone says, "Everyone took their books," the guy will get all wound up and point out that "everyone" doesn't match with "their."

Lighten up, dude. I can understand if someone writes comments about such grammar use, but to get uptight in a casual conversation? That's almost psychotic!