I am a self-confessed griefer and team killer (TKer). I have long taken part in the sadistic joys of attacking teammates in multiplayer games for mischievous fun and I am not ashamed to admit it. I do not always TK, in fact most of the time I play the game straight. But sometimes, out of boredom, I take to TKing in order to "spice things up a bit" and create some chaos.
Team killling is a well known occurrence in multiplayer games, and I have frequently been a victim of it. As a result of the rampant TKing, many games have implemented features that allow players to "votekick" someone or feature moderators or admins who can perform kicking or banning.
In America's Army, I enjoyed tossing smoke grenades in towers where snipers on my team liked to hang out, much to their outrage. Other fun included throwing flashbangs and blinding everyone on the team as they left the spawn area. Sadly, the game later implemented the punkbuster system to prevent such behavior and spoiled the fun.
Counterstrike Source has also provided me ample opportunity to exercise my evil habits. Much like America's Army, this game features a wide array of annoying grenades to toss at teammates, as well as the ability to attack a teammate with conventional weapons. My favorite pastime was finding a mark and cutting them with a knife until they had 1 health point and were sure to die. If they shot me, I would use the server's revenge feature to slay them the next round or, on some servers, turn them into a firebomb to set the entire team on fire. I recall one occasion when I joined a team of 30 people and began employing these tactics, only to have 20 of them leave in disgust. The others attempted to play on seriously with a sort of pathetic determination.
Lately, I have found great fun in the free game known as TA Spring. This game is a remake of Total Annihilation and is free to the public, plus totally unmoderated. As a result, you can TK with no holds barred and no worry of being banned. Since it is a real time strategy game, I have found amusement in capturing my teammate's buildings, nuking their base after they have spent a lot of time building, and sending crawling roach bombs to blow up their base. Of course, all of these actions are usually met with rage and the player usually leaves the game in total frustration.
Garry's Mod is another fun game for griefers. In most sandbox games, you can spawn a car and then proceed to drive around, running people over, creating gameplay reminiscent of Tarantino's "Death Proof". You can also dump 50 giant silos on a server, causing it to lag uncontrollably, or grab people's stuff with your physics gun and move it around to tease them.
Why do I commit these unspeakable crimes in online gaming? I'm not entirely sure myself, but I do know that every time I do it I laugh my ass off watching everyone's reactions. I suppose it is sort of like playing a prank since you are committing an unexpected act in order to evoke an unusual reaction. Although I will admit that TKing is annoying, it also keeps the game from getting unbearably boring and repetitive.
Imagine the surprise you will feel when you see your teammate turning to point his gun at you. Its sort of like the plot twist in a good movie when you find that a seemingly good person is really an underhanded villain working for the opposition. You generally play the game thinking that you will only have one distinct enemy, but be sure to keep an eye on everyone. Most people don't expect TKing since they get into a repetitive style of game play, thus are taken entirely by surprise when their base is attacked by a teammate and are totally unprepared for the resulting chaos.
Do not hate the TKer, just remember that they are a prankster and mean no serious harm. Although some people do it for evil purposes (such as stealing equipment in an online RPG), most of us do it as a joke. The bottom line is, don't take us too seriously and don't take the game too seriously.