To get a raw deal or the short end of the stick. Derived from the behavior of barnyard pigs. The "runt" or weakest piglet is forced to nurse on the tit farthest back on the mother pig, which gives the least nourishment.
When one has had so much sex that their cock is rubbed raw but they have sex again anyway and it burns like a motherfucker and just as they reach a climax and cum they yell, “Oh the humanity!”