One who has assigned themselves the duty of pounding the anuses of other people for the duration of their lives. The act will lead to the penis pounding into the recipient's colon, hence the name.
Man: Well honey, its off to another day drudging through the swamp asses. Its a dirty job, but someone has to do it.
Woman: Okay honey, I'll have dinner ready when you come back! I wish that being Colon Pounder didn't give you such bad Swamp Cock