Those who use terms like ‘neckbeard’ and ‘basement-dweller’ are, overwhelmingly, people in the technology trades with non-mainstream interests and some unorthodox ways of organizing their social interactions. In other words, they're prime targets for being called such themselves.
I had thought this was some self-conscious irony and been annoyed by it, as I seem to lack the capacity to enjoy satire, sarcasm, and self-conscious irony.
This morning, I realized that there's more to it than that. The main mechanism seems to be some members of a low prestige group cannibalizing other members to elevate their status. The rise of ‘geek chic’ and the esteem given to Internet startups has driven this trend forward by creating a definite position of esteem. You also see this, to a lesser extent, in other groups and subcultures.
And it's really annoying.