A suprisingly large gruesome parasite that situates itself on the overhanging skin of a persons arsehole. It lives off the juices slowly secreated through the bumhole, and its lifespan it approximatly 7.6 years! Being harmless itself, a rectum-fish can however, cause accute discomfort to its host, if it has been sitting down for long periods of time, as this restricts it's oxygen supply, making it squirm.
Man: I gotta go to the doctors' later today, I've gotta a bitch of a Rectum-fish sucking out my guts.
by Mr.Pete November 09, 2007