Driving A Destroyed Vehicle

This Halo 3 glitch allows people to ride in destroyed vehicles. Unfortunately, the name of the glitch is a misnomer -- such vehicles cannot be actively driven, only ridden in.

Grenade Method
You need two people to do this. First, go to any level or a multiplayer map and have someone (Person A) stand next to a damaged vehicle. Next, someone else (Person B) has to stick Person A with a Plasma Grenade or Spike Grenade. As soon as Person B sticks Person A, the latter has to get into the vehicle and the former has to board it. The grenade will kill the driver but not the person boarding it. The vehicle will explode and Person B will be occupying and riding the destroyed vehicle.

This method can also be done using a Spartan Laser, by Lasering the vehicle instead of sticking the driver; this is a common occurrence on Snowbound in the Lone Wolves playlist. There is, however, a greater chance of the Laser-firing player dying from the Laser's splash damage.

Banshee Method
This can be done in the Campaign level The Ark. Using a Plasma Grenade and a Brute Shot, you must attempt to destroy the Banshee that the Arbiter will get in. If done correctly, the Arbiter will be lying in the Banshee's wreckage. This same method is possible in multiplayer -- it has been reported to happen on Valhalla. When a player tries to board an enemy Banshee, and a Spartan Laser hits that Banshee, sometimes the player proceeds to drive the now-wrecked Banshee.

Banshee with Overshield Method
This also can happen if a person with an Overshield hijacks a Banshee right as the pilot rams a wall and destroys the Banshee. Instead of dying, the Overshields protect the hijacker and leave him/her riding the destroyed Banshee.

Trivia

 * This usually happens without the player's intention when they attempt to board an enemy vehicle, usually Banshee or Hornet.
 * This incident is common on larger maps with more vehicles, such as Valhalla and Avalanche.
 * The Grenade Method can be performed on Ghosts as well, though one would stick the actual vehicle instead of its pilot. A destroyed Ghost cannot shoot, but oddly, it can boost.
 * Even while flipped, the game will not take you out of the wrecked vehicle.
 * Eventually, the vehicle will vanish, as the game cleans up all wrecked vehicles when they respawn.