buttercup swamp Share definition Flag a yellow tinged, heavily infected, swollen pit of a fanny. Usally caused by one of many sti's . oh my fanny is reaking, it must be caused by that gang of tramps i let gang fuck me in that alley the other day. you fanny is a buttercup swamp buttercup swamp by Big Ant May 24, 2006 Get the buttercup swamp mug.