Crusty mustard Share definition Flag When a person has diarrhea and fails to wipe thoroughly leaving a yellowish brown crust on their ass I was fucking this one girl in the ass and notices she had some crusty mustard leftover Crusty mustard by Imfluffy September 11, 2016 0 0 Get merch Get the Crusty mustard mug. Buy Now — $32.95 See more merch