The buttstache occurs when a dude and a bitch are 69'ing and the bitch (or dude) farts directly on your lips and nose, causing the fart wind mustache "The Buttstache
friend 1: "This was fucking gross bro, I was going down on this bitch and she was suckin ma dick, all of a sudden, she ripped a fat one right on my face!" freind 2: "Ew what the fuck? It was the Buttstache"
by M-CsmackAbitch October 08, 2008