I think it’s more compulsiveness, really. Pedantry doesn’t really require self-aggrandizement or any particular belief in how awesome you are. Mostly, it’s just an… itch, really, when you see something wrong. And you have to scratch it. Sure, sometimes you can just let it slide, distract yourself with other concerns… but it’s there… and if you’re not careful, you’ll remember it, and it’ll just worry and nag at you, slowly driving you insane…
… or you just give in to that itch, and tell people exactly where they’re technically incorrect.
Narcissism, self-hate… neither one even begins to describe it.