Midway through Marathon Infinity, Tycho will get extremely angry at you for suddenly cooperating with Durandal. His reaction? "Prepare to taste vacuum, fool." He then promptly teleports you out into space. Where you sit. And wait. And shoot. Don't worry, Durandal will eventually save you.
LPer: We could take the long way... (grenade jumps, but fails to reach the ledge) ...or we could take the long way.
Many of the quotes from the Marathon Trilogy. An example: "By the way, I had an accident with some defense drones while you were away. You might bump into a few of them here. Don't worry, they're mostly harmless; I don't think I gave them any ammunition for those grenade launchers."
The screams that the BOBs make when you burn them, or other players. Funnier because Bungie encouraged players to murder the people that you were supposed to be saving.
Also, 8-Player Co-op in a game meant for one person? When it's not a ridiculous and hilarious amount of carnage, it's pure awesomeness. Why did they get rid of 8-Player Co-op?