The Average Raider
Chances are you fit into this category. He talks on Vent when needed, is fairly adaptive to the instance, pays decent attention, fufills his class role adequately, and doesn't cause too many problems.
This dude always sees the worst in things. He'll say things over Vent like "[Main Tank] is at 90%, it's a wipe" and means it. If your group wipes at all, no matter how preventable it was, he'll either leave the raid or complain that it's going to be "a long night." Even after successes, this guy will say stuff like, "that was really sloppy, we almost didn't make it."
Arch-nemesis of the pessemist, the optimist will see the silver-lining in everything. Expect to hear things like "That was a great attempt! We got Vael all the way to 29%!" and "All we need to do is keep the MTs up, do more dps, stop dying, and we've got this." Even if your raid is absolute $!@% that day, The Optimist will celebrate all accomplishments.
Swears profusely about everything. And I mean EVERYTHING. He'll swear when your group is idle in front of the two beginning giants. This dude can be very funny, especially if he has an accent. He's almost always drunk and will suually tell you he's drunk multiple times.
Provides good entertainment for your raid. Does impressions, tells jokes, sings/raps, plays sound clips... you name it, this guy does it over Vent. His main flaw is that he will do this at the worst times, including in the middle of boss fights. This guy can overlap quite easily with The Cusser.
Damn, I hate this guy. Every time your group wipes he will immediately try and blame someone and/or anyone. If he makes a mistake, he'll come up with some BS excuse for it ("I lagged into Ragnaros; that's why I pulled aggro!", etc.) At least one wipe he will claim that it was your class that caused it, even when it was probably his class too. Example: Your raid gets to Onyxia. Your warlocks don't bother with an SS, being told that anyone who rezzes will pull aggro on Onyxia and that SSes are useless for wipe-control. Mid-fight the main tank dies, druids have no battle rez. Your group wipes. The @$%!@%&, a druid, immediately starts screaming that the warlocks are incompetent for not placing a soulstone. A warlock asks him why the MT wasn't battle-rezzed; he replies that "all the battle-rezzes were used on mages." He then continues to blame the warlocks. (This actually happened to me.) He's probably buddies with at least one officer, if not an officer himself. Tends to overlap with The Pessimist.
NOTE: This does not describe all female players, only a certain breed of them.
The Princess will flirt with everyone, and I mean EVERYONE. She almost always gets loot over people with more dkp, due to either her flirting with all the people above her or a "slip-up" by the Master-Looter. If she's decent-looking, everyone knows what her Myspace is. If she isn't decent-looking, she'll pretend she is. She probably talks in a really high-pitched voice. She knows at least one other raider in RL and will defend him on any issue no matter what; the whole raid will probably start taking his side too to suck up to The Princess.
Mid-battle will start screaming about anything that happens to him or to the raid in general. Some of his favorite lines: "I'm mind-controlled! HELP! HELP!" on Luci, "PRIEST DOWN!" repeatedly, "I'M DEAD, BATTLE-REZ ME!" if he's a rogue, "ADD UNSHEEPED!" on Domo, etc. Usually the $!@% he complains about isn't anything worth worrying about.
The Vent/DKP !@#@
Constantly suggests that Vent-talk should be muted for everyone but the Main Tank. Hordes his dkp like mad and won't work with you on any item (ex: he has an epic belt and you have a green belt, your class belt drops, he takes it despite you asking if you can work something out). Amazingly, tends to have more dkp and less items than anyone in the raid, somehow.
The AFK guy
NOTE: This is pretty much me.
Is AFK during EVERYTHING. He's rarely in Vent (to listen for boss fights) even if he is at his keyboard, and he usually isn't. Typically places himself on Follow to avoid people noticing. He's $!@% last for his class on the Damage/Healing meter and never does his class job. He's usually there in time for boss fights but will probably alt+tab again after the fight is done and loot has been distributed. When confronted on his bad DPS, he'll come up with an excuse ("I'm a fire mage/shadow priest/feral druid/not geared/on the phone/bad connection!").
Will pass on everything they can use, even if it's a big upgrade for them, because "someone else can use it more." If this person is a mage, there's a good chance he's saving up for a Mageblade.
The Quiet Guy
Never talks on Vent, ever. If he has a mic, it's probably dusty as hell. When he talks, the things he says are so funny that you'll wonder why he doesn't talk more often.
The Damage Meter Obsessive-Compulsive
Obsesses over being #1 on the damage/healing meters. Re-syncs everyone's meters after every boss and every other trash mob. Only stops after being threatened with no loot and/or a /gkick, then reverts to his old ways on the next run. Has no sense of caution on any fight and will ignore or disobey orders to stop attacking when aggro is an issue. Does other stupid things like crazy healings on Razor phase one, backstab-spamming the offtank's target, etc.
The Loot !@!#&
Complains often that he never gets loot. Usually tries to use a pathetic appeal to get other people in his class to pass on items he wants. Is usually well-geared despite what what he presents. Will bid on EVERYTHING without scruples, usually getting them because no one wanted, and usually has the lowest dkp in the raid.
The Guy That Yells Too Damn Loud
Can't ever control his volume in Vent. Good, Bad, whatever the situation is he's probably screaming loudly about it. If he fiddles with his outbound, either you won't hear him at all or your speakers/headphones will !&$%ing explode.
"Then, to hide their frailty, they hurt those who are kind.
I whisper farewell to this ugly world and dance nimbly with brilliant wings of red."