It's an insult, so it's sort-of exclusionary by default. It refers to those nerdy guys who don't know how to dress themselves, compulsively collect arcane knowledge and probably smell bad.

Maybe we ought to come up with a female stereotype to match, or a genderless one. Or maybe this will do just fine - you don't want to be a 'neckbeard' regardless of gender, it's not a good thing.