A sexually discomfiting prank whereby the actor, in the presence of several others in a confined area (such as an elevator), covers his crotch and proceeds to slowly and steadily approach the victim,
impressing his pelvic region upon him, moaning and assuming the blank
expression of the walking undead (i.e., a zombie).
The purpose of this is to annoy the victim while providing amusement for friends or bystanders within the confined area. If more than one person joins in on the proceedings, it becomes a crotch zombie swarm.
The purpose of covering the actual crotch with one's hands is to provide a physical bulwark of
heterosexuality, or no homo.