BALLS TO THE DOME
Since the dawn of graphically advanced online multiplayer games, players have been crouching on one another's faces to imitate the act of dipping one's balls into another's mouth, like a bag of fine black tea in a hot, dead cup of water. Hence: teabagging.
Some developers would rather not acknowledge that this frankly weird practice occurs at all, but 343 instead paid tribute to its fans and all their debauchery. Just send an armor ability hologram out over a dead spartan on the ground and see what happens.