In Halo 2, there is a glitch in which you can kill yourself with a Battle Rifle. It works best on SWAT (or a gametype with no shields and Battle Rifles).
Performing
Type 1
Aim straight at the ground with your Battle Rifle and walk forward. The projectiles will hit the foot and be considered a suicide (similar to sticking one's own foot with a grenade).
Type 2
It is also for one to shoot themselves in the head. Run and shoot twice straight ahead, then switch weapons. If performed quickly, the ammo will hit the firer in the head for an instant death.(This is a variation of the Guardian Glitch)