I think it's pretty much all about self-image, jealousy and sexual frustration.

It's pretty much agreed upon that this nerd hate comes primarily (if not entirely) from men. I'll just be blunt. I assume a guy who sees a "fake geek girl" and lashes out over it is only because he finds the whole situation unfair. I figure he's thinking "you like comics and games? I'm OBSESSED with comics and games. You should be impressed. Why is it that you like the THINGS I like but not ME specifically?"