How about some common forum types, observed by yours truly:

Trolls. Not trolls themselves, but the word. It's so vague, I've never really understood what a troll is meant to be. "Someone looking for an argument?" Come on, it's a forum, the main reason people come here is to argue in the first place and you can't call someone a troll based merely on that. You do have a point when this person shows no personality other than wanting to argue, but it's still not a huge problem. People that call each other trolls should just kill each other. I'd like that.
Prime example of a real troll: sitboy.

Boring, Noisy Fuckers. What's worse than someone who's out for an argument all the time? Someone who NEVER says anything slightly useful. They make posts that aren't even useful, they just talk a lot and never make any useful points. Scrolling fodder. You feel like they've just wasted your time. A lot of these on a forum can really take the spark of life out of the place. "I agree,", "lol", or the worst kind of Boring Noisy Fucker - a long post that says nothing.
Prime example of a Boring Noisy Fucker: Leo Volont.

Bong Man and Bong Lady. Metaphysics, psi-balls, all of that. I really have trouble taking these kind of people seriously. I just can't. I have to laugh. And try not to breathe in whatever they're smoking. Probably solvents. Often congregate in groups, you know, so the fumes (from both their arguments and whatever drug they're using) become all the more overpowering.
Prime example of Bong Man/Bong Lady: Beyond Dreaming anyone?

Tough Guy. Can't resist swearing at every opportunity, tries to be Maddox and fails, says that everything "needs to be punched in the balls". Hates gay people, hates anything, to be honest, you have to wonder why they even bother coming to a forum when you could just put their argument as simply as "I hate ______ and think they need a kick up the ass". Really, we're all impressed. When confronted, threaten to kill you. With no address. Or ability to spell.
Prime example of Tough Guy: Let's go with...Techboy.

Rebel Without A Clue. People who are angry with the administration because they're the administration, or can't deal with the fact that there's actually some degree of moderation on the board. That's not to say I don't have my own beef with the administration at points, that's perfectly fine, but it would be really nice if you A) had a reason and B) made it clear instead of concocting silly, childish little plans that will never come to fruition to "take over the forum". Really, this is a forum, not a playground.
Prime example of Rebel Without A Clue: Oh, they'd kill me if I mentioned any names.

Overly Sensitive People Who Show Absolutely No Signs Of Ever Growing A Thicker Skin. I'm sarcastic, yes, and I'm often prone to tell people straight up what I don't like about them and so on. This is not a huge problem. But what really gets me is when I find people who get offended by any little thing, or who spend more time crying about what someone said and feeling insecure than being part of the forum. It's the internet. If you don't like what someone said, don't reply to it, or just ignore the person. Really. Nobody's forcing you. Of course, use common sense.
Prime example of an Overly Sensitive Person Who Shows Absolutely No Signs Of Ever Growing A Thicker Skin: well, I obviously can't answer that one.

Date Line Man/Woman/Eunuch. The forum is not your hookup place. The forum is not your hookup place. No, no, stop making sexual innuendos in every other post! Stop creating sex harems, sorry, groups of friends! Stop using your boobies or penis to influence the weaker minded peons! JUST STOP! The best part is when a Date Liner can't actually get anyone in the least sexually attracted to them. It's just painful to watch, but funny nonetheless.
Prime example of a Date Line Man/Woman/Eunuch: nameless

Airhead Savant. The kind of person that thinks they're really good at something and wants everyone else to know about it too. Takes any opportunity to be as condescending as possible, and yet never quite reaching that point where you can call them out on it. Often so smug you want to telepathically punch them in the face, just to see if Smart Guy saw that coming. What's worse, they don't actually know anything. They just pretend they do, or copy crap from Google and Wikipedia that makes them look like they do.
Prime example of Airhead Savant: Damn, I regret examples now. You take a guess.

Autistic Airhead Savant. Same as above, except they also happen to have self diagnosed themselves with OCD, ADHD or some other pop culture psychological disease (that makes those who really have the disease have a much harder time explaining themselves). This makes them all the more clever, apparently.
Prime example of Autistic Airhead Savant: God, just look anywhere.

Interior Decorators/Grapists. I don't like it when people abuse the formatting facilities. To be honest, I don't see why forums should even provide facilities for you to write your text in a different colour or, even worse, a different font. One person on their own is not overly obnoxious. One largish signature is OK. But soon the problem snowballs and you've got a thousand flashing neon coloured things on forums from users who have followed suit. It starts to look like eBay with "L@@K" and god knows what else. What's worse, interior decorators get really mad when you ask them to restrict their artistic license a bit.
Prime example of an Interior Decorators/Grapist: Casualtie. He stopped. Ivey likes to colour things in green. But she's OK, she's a special exception. Ivey, ivy, green, y'know? It's an obligation, comes with the name.

The Hilarious Avatar Pirate. Yeah, OK, it was funny the first time, but when you "impersonate" someone by merely taking their avatar, you're not doing anything except being a thinly veiled attention whore. Just don't. You're not even original in the avatar pirate getup: it's been done before.
Prime example of a Hilarious Avatar Pirate: er, werburn?