Fatty Plumpkin Share definition Flag Noun) 1. An abnormally obese anus. Ex. Badonkadonk 2. An anus which is utterly large in volume. The women was not shy about her fatty plumpkin: she wore a pink thong viewable to everyone behind her. Fatty Plumpkin by Cornelius the Bad-Ass Pigeon June 11, 2008 0 0 Get merch Get the Fatty Plumpkin mug. Buy Now — $32.95 See more merch