Another word for anal intercourse.
I.e. the insertion of the erect penis into the rectum through the anus.
Buttfuxx gives a special feeling of greater power to some people while penetrating.
It can also be considered as an act of (anal)domination.
1. Horny stud: "Hey girl, wanna buttfuxx?
Straight into your asshole?"
Frigid girl: "Eeooohw, you pervert leave me alone!"
2. Person 1: "Did you know that 2 out of 5 women
are addicted to buttfuxx?"
Person 2: "Oh, really? I guess I should deliver
some hard buttfuxx to my wife then and if
she's lucky I'll even use anal-lubricant