When a man sticks his thumb up the females rectum, and as she opens her mouth in shock, he pisses in her mouth. This will then cause the dripping to occur, and the hitchhiker part is obvious.
i was gonna break up with this chick and found out she cheated on me, so instead of telling her i knew, i gave her The Dripping Hitchhikerand then left...
(Noun) To anally fist a woman with one's thumb extended fully up, as if hitchhiking.*
*(The main difference between this and other 'definitions' of this term is that with a true 'Hitchhiker' the fist and upright thumb must be fully inserted. This is not a 'Shocker'.)