The Meaning of Life, the Universe, and Everything.
Flame - verb - a post pointing out the logical fallacies and/or factual errors in another user's post
Spam -noun - humor that the mods don't find funny
Troll - noun - user who disagrees with the mods
User - noun - someone who has nothing better to do than argue with random anonymous strangers on the Internet
Mod - noun - someone who has nothing better to do than settle other people's arguments on the Internet
Sockpuppet - noun - user who is willing to risk an IP ban just to "win" whatever argument they are having right now with random anonymous strangers on the Internet
Astroturf - verb - creating sockpuppets specifically to give the illusion of winning an argument with random anonymous strangers on the Internet even if your main account hasn't been suspended or banned
Suspend - verb - temporarily force a troll to use a sockpuppet
Ban - verb - permanently force a troll to use a sockpuppet
IP ban - verb - force a troll to log into their sockpuppet from a different computer
Admin - noun - someone with whom you should not have an argument on the Internet
Add your own!
EDIT: New additions!
Fascist - noun - someone whose political ideology differs from your own (suggested on another forum)
Brony - noun - a 30-year-old gay man who creates pornographic fanart and/or fanfiction based on a TV show aimed at 8-year-old girls (inspired by Bbqpizza)
Anti-brony - noun - user who is somewhat annoyed at having ponies shoved in his/her face every time he/she visits a forum (inspired by jmm98)
Pegasister - noun - an 8-year-old girl who watches cartoons that are aimed at her demographic, and who then gets on with her life instead of pasting ponies all over the Internet (inspired by SkylordCentral)
1337 - noun - The type of speech used by complete noobs. (contributed by Spongeblock)
Pr0n - noun - The 1337 version of pornography. Also used for unsuccessfully evading search filters.(contributed by Spongeblock)
Pwn - Verb - win an argument with an anonymous stranger on the Internet