"Pwned" - A corruption of the word "Owned." This originated in an online game called Warcraft, where a map designer misspelled "owned." When the computer beat a player, it was supposed to say, so-and-so "has been owned." Instead, it said, so-and-so "has been pwned." May also be used to your friends when they lose their keys, drop a cell phone or spill coffee on their new pants.
"W00t" - "w00t" was originally a truncated expression common among players of Dungeons and Dragons tabletop role-playing game for "Wow, loot!" Thus the term passed into the net-culture where it thrived in videogame communities and lost its original meaning and is used simply as a term of excitement and extreme nerdiness.
"I defeated the dark sorcerer! Woot!"
"Teabagged" - A traditional saying in shooters, after you get killed or owned, the enemy begins to crouch up and down on your dead body, whether over your head or other preferred area of the corpse. Makes great kill-cam footage.
"You got served!" - Another way of saying "You just got owned" or "Pwned!" or "You suck at breakdancing!"
"ZOMG HAXX" - Two separate words, 'zomg' is derived from 'omg' meaning oh my god. 'zomg' puts an extra ZO in it, so it sounds like ZOH-MAI-GOHDUH. 'Hax' is commonly used on the Xbox Live world as a defense mechanism for people with low self-esteem who need to justify getting beat by accusing the opposing player for cheating. In conclusion, 'ZOMG HAX' means to be incredibly excited/confused/depressed about losing a game or your pathetic life, in general.
"N00b" - An insult term referring to someone who is new to a game - but is more widely used as a general insult. Usually gets spouted by an elitist, or bad players that can't accept losing (and calls everyone else 'noobs' for beating him). The videogame world's version of a rookie.
"Kekeke" - It's what some Koreans say in online games, usually signifies joy, or sometimes it's like a war-cry. You'll see this from an enemy if he is killing you, he is Korean, or both.
ATTACK THE BASE! KEKEKE!!!"
"Suxxor" - Modified version of the verb "to suck", and the meaning is roughly the same. There are two main uses, as a verb ("Dude, that suxxorz!") and as a noun ("You are teh suxxor."). They appear independently. The verb version is antonymous to roxxor ("to rock"), and a noun could be considered as a counterpart to "haxor" ("hacker"). The pronunciation is "suck-zor". Contrary to some claims, EverQuest's spell "Succor" has nothing to do with that word (actually pronounced "Soo-kore"). This is one of the early uses of the -zor word-ending. Don't say this to your girlfriend.
"Base raping" - When a team has captured all of the bases but one. Members of that team surround the last remaining spawn point and decimate the team with additional kills, insults. Note: Being base-raped sux.
"Ridicapwned" - When someone pwns someone....but it's ridiculous.
"Janitor" - Someone who avoids the main battle and cleans up on wounded survivors to finish them off.
"Muhahahaha" - Evil laugh.
"The Rocks" - Rocket launcher in Halo2.
"Bring a baggie fo ya teef - You just got assassinated.
"Boomstick" - Shotgun.
"Blue Screen Bitches" - Quitters.
"No-scoped" - A single shot sniper kill without the use of sights or a scope.