A person who professionaly rides horse testicles in races.
Carl is a testicle jockey.
Taking one deep, so deep as it appears that person is a horse jockey on a pair of testicles. Typically is used to refer to a homo, a friend who is being a douche, or a slam piece.
Person1: "Fat Alex almost seems like a mezza fanook"
Person2: "No, Fat Alex is without a doubt a testicle jockey"