When two homosexual biological brothers engage in incestuous buttsex.
Me an' mah bro are gonna do us some Mississippi Muddin' toonight!
Anal sex while driving. Especially on a long trip.
"How was the drive up?"
"Pretty good, we did some muddin' on the freeway."
Muddin (verb)
The act of one draggin their big ol hog shaft through your tight little hole
Me and the boys were out muddin yesterday