Flyboy

This glitch can be done on the Multiplayer map, Coagulation. It requires two players (one of which needs an Energy Sword), one Warthog, and one Banshee.

Directions
Have one player with an Energy Sword sit in the passenger seat of a Warthog, have the other player buzz you with a Banshee. As it flies over, slash at it when the reticule turns red, then get out of the Warthog. You should zoom after the Banshee for quite a few feet.