bumtart Share definition Flag a tart that is most-definitely made out of bum. (this refers to a gluteus maximus made into a pastry). it taste like lose. you, good sir are A BUMTART, and i shall not speak with you. bumtart by Baffle-boy January 5, 2010 0 0 Get merch Get the bumtart mug. Buy Now — $32.95 See more merch