2.) One of the four leaders of the Federation of Asshole Gamers (F@G). Is known as XBL Number 1's Deranker and for betraying.
A deranker is someone who purposely loses or sabotages a game so that his or her rank will go down. After they do it enough, they will face opposition that can't compete with them and they'll win much more often. Thus making the deranker feel better about their own pathetic life.
Derankers often will betray or teamkill to get the results they want. Luckily, in Halo 3 and beyond, Bungie made it more difficult for a deranker to prevail (no more negative suicide points, or placing the bomb outside of the map).
When you're a lower level player and there is a deranker on the opposite team, it is usually extremely obvious as they will be considerbly better then everyone else in the game. You will be able to tell that they shouldn't be in the same game as you. Derankers often taunt and make fun of their opponents after they kill or beat them, acting as if they've earned some sort of bragging right- when in reality, they've earned nothing but to get labeled a noob.
Players also derank so that they can play with their higher level friends and thus make matchmaking system bring in lower levels for a easier victory. Derankers are also called Delevelers. Deranking is frowned upon obviously, but it is seemingly not cheating or breaking terms of service because Bungie does very little to punish these players.
Legit lower level player: Get a life.