Humans in general annoy me.
However, if I were to pick special people out, I'd say "Pushy salespeople" and "Evangelists" What I mean by the latter isn't confined to religion. As much as JW's at my door worried that my soul will be anahiliated if I don't join their church annoy me, pushy anti-theists on the Internet who treat me (and others) like we're inferior, worthless and not-really human because we're not one of them, either, really freakin' annoy me. I don't think that problem can be solved, however, as I think certain folk base their identities on being "better than you" and to try to tell them that they are "likewise a sinner" or "likewise subject to mistakes and lapses in logic" due to a shared humanity falls on deaf ears. "Evangelism" for me also takes on another form - that of friends finding some shiny new fandom or thing that they are really, really into and they try to push it on me, despite my being uninterested. I may even try the thing, just on their recommend, but not get hooked from the first episode/level/chapter, but still have to contend with them not shutting up about it and treating me as though I were as totally into it as they are despite my trying to tell them otherwise.
I lost a friend in part due to her obession with yaoi, subtext and sex in general, when she didn't quite get that I found her constant dirty jokes in her AIM conversations and her attempts to convert me to every couple she fell in love with annoying. She got offended when I tried to bring her back to reality (some of her subtext-proof of couples being "canon" were... well, um... schitzoprhenic for lack of a better term. I don't think she actually suffered the disease, but she made me wonder). The breakup of the online friendship came from a general lack of respect between us (she treated me as a kind of servant...) But, yeah, overzealous fandom-evangelism was a part of it.
Pushy salespeople are the same way, although they've actually caused me to lose money. I mean, I'm awkward with other people, so when I'm in a store and someone's got me cornered, it's like a deer in the headlights syndrome and I'll almost buy whatever they're trying to sell to get them to leave me alone and let me go. I tend to call for my fiancee' or whatever friends I'm with to HELP ME! when that happens. I don't make any large purchases without someone at my side.