do a sit-up Share definition Flag insult delivered to that fat douche bag who just won't shut the fuck up fat douche bag: dude you can't do that for shitmaddog: go do a sit-up you fat shit do a sit-up by DUDL3Y February 16, 2010 0 0 Get merch Get the do a sit-up mug. Buy Now — $32.95 See more merch