To weaken or make less dangerous. Taken from the "Nerf" brand name, which makes sports equipment toys out of a soft foam (e.g., the Nerf football is soft foam rather than the hard leather of a real football). Used frequently in the context of computer game balance changes.
"The chaingun was awesome til they nerfed it, now you can't hit shit with it."
Onling gaming term for "team killer" or "team killing". Used verbally as well as in typing. The act of killing your own teammate rather than the enemy.
"The guy was blocking the door so I had to TK him".
One who exploits. In computer games, it refers to someone who takes advantages of bugs or design flaws to gain an advantage. aka "cheaters".
"That guild is nothing but exploiters, they found some bug that gave them a bazaillion gold coins."
In online gaming, the act of working with your friends on the enemy team to the detriment of your own team.
"I was trying to kill this guy but some crossteaming bitch kept healing him."
In onling gaming, something which is particularly good at causing grief to other players, especially ones own teammates.
"This grenade launcher is nice, but it sure is griefirific."
In online gaming, someone who purposely seeks to annoy the other players, especially his own teammates. Usually a griefer is someone who is not good at the game, has a poor internet connection and wants to vent frustration.
"This server is nothing but a bunch of griefer TK's. Let's go somewhere else."