When it comes to the whole Nerd Girl thing, while it can be sexist as all fuck, I can see why some nerds would get upset. I know there are girls just as nerdy as I am who are attractive, I personally know a few, but in some circles the word "nerd" has ceased to really mean anything. Any girl with glasses can claim to be a nerd.
There are even businesses to take advantage of this that are aimed at nerdy guys, who I freely admit can be dragged around by their erections a lot.
So I don't think it was rooted in sexism, more in fears of culture co-opting; that is, mimicking the superficial bits of geek and nerd culture without having any of the deeper stuff. It especially burns to see it co-opted by the people who historically bullied geeks and nerds, but that's a whole other topic.
That said, there are definitely ways it can be made sexist, and I'd rather not have defense of a culture that I share be tainted by sexism.
Edited for clarification.