A phrase “Rage Quit” has been heard a lot lately in the lobbies of MW3 spoken by players who witness a player or group of players leaving during a game or intermission because they are getting hammered. Often the rage quit is preceded by epithets and colorful language. If you are in a good clan or group of players you get to watch lots of rage quitting every time you play.
Another interesting occurrence is when an enemy mic can be heard for a brief moment after you kill them. Your entire team cannot here them but the player who made the kill can hear the remarks and these remarks are often wonderfully funny sound bites.