There are many ways to kill yourself on multi-player mode. Go to a level that has ceilings, preferably Rat Race. Get a plasma grenade, aim straight up, and throw it. Do not move. It will fall and stick to you, eventually blowing up and killing you. Another way is to have two plasma grenades. Toss the first one about ten feet from you then immediately throw another one about a foot in front of the other. Line yourself up with them. The second plasma grenade will be blown into you. Another way is to make a game play option where there are no shields and all shotguns. Go to a level with stationary Covenant shields, then get as close to one as you can with a shotgun. Shoot the shield and you will die.