ass it up Share definition Flag When someone comes to your house and farts all over the place. Even one fart can be considered assing it up. That motherfucker done came to my crib and assed it up in my motherfuckin' heezy! ass it up by Uncle Funkalunkel October 15, 2003 0 0 Get merch Get the ass it up mug. Buy Now — $32.95 See more merch