Used to refer to the penis and scrotum as a single unit. Its name derives from the fact that a profile view of a cock and balls crudely resembles a hammer, with the scrotum as its head and the penis as its handle.
Guy #1: Hey I was going through John's mail and I found this issue of "Cock'n'Balls Monthly" with his name and address on it.
Guy#2: (flipping through magazine) By the looks of it, they really cater to the package shot
Guy #1: Well we all know what a big fan he is of the donkey hammer.
Guy #2: True, true.