On a level where you can find a group of five or more marines (such as Assault On The Control Room), kill three marines quickly. The remaining marines will call you a traitor (shouting things like "He's loco!") and will start firing at you. If you shoot them, sometimes they will ask you if they owe you money or tell you to clean the mud off your visor. Also, after being considered a traitor, if you want to regain the Marines' trust, find some Covenant and kill them. If you kill enough of them, the Motion Tracker will show Yellow-Green points where your "fellow" Marines are and they will not shoot you, though they may aim at you. Note: This was done in the Halo level.