"Fake Geek Girls" don't exist. Simple as that - there aren't insecure pretty girls preying on nerdy men in conventions, and in the rare example where there might be, it'd pretty hypocritical for geek culture to take offense.
The thing is, where geekdom, nerddom, gaming and more used to be the realm or socially insecure boys (sad but true), all of the development and quality within these areas have helped explode them into the mainstream as a premium form of entertainment. So yes, girls (even pretty ones) are getting involved, and are damn welcome to in my opinion. The fact that encyclopedic knowledge and commitment to anything "geek" isn't a priority to some of these girls seems to be the biggest bugbear of all, but again it's a sexist one. I love drawing and reading comics, I am contributing to a computer games site, and I play boardgames. I also work in global human resourcing for the biggest professional services company in the world... not very geek. I'm also a sports fan, and enjoy activities with my family. Geek isn't my whole world, but because I'm a man, people don't even think to question it.
As for the adverts of Zooey Deschanel or the demotivational posters... you do realise that those are posed photos, right? As in, those are faces for hire, bought by marketing execs because they know that you, like all other men, are happiest when pandered to via the lowest common denominator. So are you angry at these girls, or at yourselves, for not being the intellectual post-human powerhouses of logical thought that you make yourselves out to be, but rather the same, hormone and genetically controlled animal that we all are? Must be disappointing, hence newest nerd rage.