To be honest, it depends on what the girl thinks makes her a geek. But everyone else has already discussed this point so I'm going to take it in a different direction. Note that I'm really only going to be talking about gamers right now, I'm too pressed for time to consider the entire wonderful spectrum of nerd culture:-
These 'poser' geek girls are not alone. I've come across plenty of guys (probably more of them than the girls actually) who have only a very casual interest in say..Mario Kart, or an equally widespread game, yet call themselves a geek or a nerd. These guys and girls perhaps only really play one or two games with their friends, and sure, they may know all the catchphrases, but that's only because they're so embedded in pop culture at the moment. The 'posers' have the capacity to become real geeks if their interest becomes deeper but usually they stay shallow and label themselves 'geek' to seem quirky and interesting. There's no point taking offense at it, they're only human after all and every single one of us has tried at one point or another to make ourselves seem intriguing. Just ignore them or expose the depths of your own geekiness, they'll soon realise they're out of their depth and 'nerd up' or just leave, either way it'll solve your problem.
Back to my point about guys being just as bad. In my experience it tends to be guys who're more guilty of this. Sure, there are the girls who're God-awful at gaming and think they're all that, but you just ignore them. It's harder though with the guys who spend their evenings playing exclusively mainstream games (maybe even just the one), such as COD, and think this constitutes nerdiness. Whenever I've got into a conversation with one of these guys who's been trying to impress me with his gaming I find that they genuinely believe having seen Star Wars once or twice and invested in an EcksBawks makes them unusual.
In short, posers suck, geeks rule.
