buttwank
putting your manhood between the cheeks of a girl with a big ass and goin for it, similar to a tit wank but with a butt
alex didnt want anal but allowed tom to give him a buttwank
Buttwank
The act of sexually stimulating one's anal region by the use of a dildo. Also refers to anal sex, whether it's gay or not.
The guy from the pen was horny in the ass so he decided to give himself a buttwank by carving a dildo out of a bar of wet soap and beating his ass with it repeatedly.