bum gravy Share definition Flag the morning after a major booze fest you might splatter the pan with bum gravy/ass water/diarrhoea. my guts were rotten this morning, i had a major case of bum gravy bum gravy by steven bakewell August 10, 2006 0 0 Get merch Get the bum gravy mug. Buy Now — $32.95 See more merch