It is a nickname given by
homosexual cowboys from the south to their fellow gay cowboys from the north. It comes from William Tecumseh
Sherman, a Union general during the Civil
War's nickname, cump, and cum dumpster. It is used as a flirty way to get into another cowboy's pants at the ranch.
Ceejay: Shucks, Andy, gonna make you into my Cump
Dumpster when you come down to
Atlanta.
Grant: Dang twang, fill my
butthole with your cum, boy.