Rigorous Butt Sex-
1.Intense, mostly pleasurable but possibly painful(for either party) anal sex. Mostly used as a humorous example rather than an enticing possibility.
2.A fierce display of buttsexery
3.also Roast Beef Sandwich(how Arbys got its name)
(word origins attributed to Zeb)
"at first she was scared, but after I showed her how, she's been begging me for the R.B.S.
"You gotta have an ass of steel to handle my R.B.S"