Corpse humping

Corpse-humping or teabagging refers to the act of repeatedly crouching over the dead body of a killed enemy, intended to mimic a sexual act. Online players teabag most frequently as a "victory dance" to insult and aggravate the victim. Doing so, however, can distract the performer from their surroundings, leaving them open to death from another player or the victim (after having respawned).

Overview
The crouching action was originally created for the purpose of avoiding getting hit or to hide, but online players mostly use the feature for teabagging. An alternative to teabagging could be punching or shooting the body, just after the victim was killed.

The action of teabagging (albeit without a corpse) is also sometimes performed to egg on opposing players; in these situations, the crouching player is effectively saying "come and get me", with the intent that the opposing player will come closer and be killed.

Trivia

 * In Halo 3 and ODST, Bungie included a "dead reflex" so when a player teabags the head of a dead opponent, the opponent's head moves up to the player's crotch. In contrast, Halo 2's reflex was only to move up and down, while in Combat Evolved, there was no change or head movement whatsoever.
 * After the Prophet of Truth is killed in Halo 3, his corpse can be teabagged. Doing this will cause him to fall through the platform he is on. You can still see him under the platform, but you cannot reach him. If you kill the two Elite Combat Forms on the platform and teabag them, their corpses will also fall through the platform.
 * In Halo 4, projecting a hologram onto a corpse will make the hologram hump it. Similarly, the Mantis bipedal walker is capable of crouching, much like an unarmored SPARTAN; while this maneuver's usefulness is somewhat negated by the Mantis' large size, the motion allows you to teabag dead opponents while you're still driving the vehicle.