Trunkbutt is the slang term for a prolapsed rectum. This unpleasant, and unsightly condition can be caused by health reasons (specifically bacterial infections) or sexual overuse of the rectum through anal intercourse. In the case of sexually caused trunkbutt, the pulling motions of the penis or other phallic object causes the ring of muscles of the anus to protrude outward. The reality is that this malady looks nothing like an elephant's trunk, but because of the cylindrical shape, it is compared to one.