hackers, glitchers & scammers, i mean i use a glitch every now and then, but i never use it in connection with a public game, i just do it on near empty games when i'm bored and everyone's waitiong for more people.
sore losers, the type that swear way too much, calling you gay and stuff, though it is occasionally hilarious to listen to, when you get killed it's okay to swear at your killer once in good fun, possibly phrased with a "XD" to make that point clear, but a lot of people are overly serious, hurling insults childishly.
those that accuse you of cheating when you kill them, this is just plain annoying, if you die you respawn and try again, throwing out accusations like that are just a drag on the game quality, wether the person hacked or not, you shouldn't bother accusing them, if they hack they'll eventually make it known to the host who can either kick him or stop the game.
rage quitters or just plain quitters, if you join a game i'm one of those people who say you should at least stay until the end of the game, if you get killed and quit because of that it's just weak, even if the players there are out of your league in terms of skill you should still make a good go of it, if you aren't comfortable after one match, then leave, going ballistic with insults and leaving or just leaving when your team is losing is just stupid but in the end it's your choice to leave or not, just do it quietly without upsetting anyone's gaming experience.
complainers, those that complain when you use for example, a banshee in halo (the original) now i personally think they overpowered it a bit but i don't let that discourage me, i don't have a hissie fit over it, no i just play on as normal, now i can understand complaining if that person refuses to take part WITHOUT said vehicle or weapon (eg. rocket launcher) because it's then obvious that they just want to use the most powerful stuff. (for the record it is satisfying when you take down said banshee with just a pistol XD) oh yeah, not to mention people who comlain about campers, IT'S A VALID TACTIC, find a way around it, they're not freaking invincible
oh yeah, team changers, now i don't mean team changing at the start of the game, no i mean the people who switch teams to be with the strongest players, or when their team is losing, i mean, the game is for fun, not winning or losing, pick a team, and stick with it and don't cry if you lose, you tried and lost, rise up and try again next game.
i probably didn't cover everything and i'm not gonna try, this is long enough already, if i have encased anyone in this thread with any of the above (i beleive i have done a few people who have issues with camping) feel free to oppose me on the matter, i camp every now and then, i'm not brillient at it but it breaks up the normal routine of 'sneak in, wait for optimal kill possibilities then go nuts', that as well as going with a few other guys and helping them survive and conquer. (oh, most of this is ascribed just to the original halo, only non rts/MMORPG that i have to play online, nothing else has really grabbed me yet XD)
...i'm talking too much, end post! >.<