Drive an AA Wraith
From Halopedia, the Halo wiki
It is to be noted, however, that the Wraith will self-destruct once you leave it. Avoid leaving the Arbiter or any Marine in the turret; they will die when the vehicle self-destructs, and the deaths will be counted as betrayals.
Anti-Air Wraiths and, in Halo 3: ODST, normal Wraiths cannot normally be piloted because of a function Bungie attached to the vehicle: when the driver dies or exits, the vehicle self-destructs. This is why killing the driver before completing the glitch prevents it from working, and why the vehicle self-destructs when a player exits the cockpit.
The glitch that allows players to pilot an Anti-Air Wraith is a timing exploit. If a player kills the driver while holding RB, they will enter the vehicle the moment the driver dies—and before the vehicle self-destructs. The span of time at which the vehicle is pilot-less will be so brief that the game will fail to notice it, and thus will not destroy the vehicle.
There are some problem areas with this glitch. In particular, hijacking an Anti-Air Wraith becomes nearly impossible if the Wraith notices the player. If the player manages to jump onto the Wraith without being shot or splattered, the Wraith will continuously drive and back up in a circular motion, attempting to escape. Such erratic movements make it extremely difficult to keep a steady aim on the driver's head, and impossible to position oneself so that the "Hold RB to board Wraith" prompt does not appear. A player can counter this by stopping the vehicle with a Plasma Pistol overcharge or a Power Drain.
In cooperative play, two players (Person A and Person B) can cooperate to perform the glitch. On Local play, it does not matter which player acts out which role. On Xbox Live, however, only the host can act as Person A; if a client player acts as Person A, then at best they may end up "driving" the vehicle after it has exploded.
This method addresses the problem of accidentally boarding the Wraith when trying to drive it. By boarding the Wraith, Person B prevents Person A from accidentally doing the same. This guarantees that when Person A holds RB, they will enter the vehicle and pilot it.
Note that the Wraith will still explode when Person A exits it—even if another player is manning the turret.