Typekill (verb): To kill someone in a First Person Shooter while they are typing a chat message. A typekiller is one who does this.

Ignorant n00bs shout this when killed in such a situation, when they should have been more worried about finding a safe location to type, or actually playing, but they bitch at someone who might have snuck up on them from behind (so the typekillee might have died anyway even if "alert"), or shot first and asked questions later.

Most likely, saying "Typekiller" was made popular by Quake 3, which featured an unmistakable blue box with a ;) over the head of someone that was currently typing. In this way, there could be no excuse of "I didn't know you were typing"

This all has something to do with "honorable combat," which is an oxymoron unless you still live in the Middle Ages. The Code of Chivalry was kind of forgotten when knights were replaced by M40A1's and SAW's.

When you eat dirt for the first time and leave your family to build a shack in the woods

One who takes advantage of online players who cannot type as fast and/or do not have a voice headset to speak on, and kills them while they are in the process of typing out a message. Not to be confused with a TK'er, which means something totally different.