The proper name of any kind of food that will make one's butt fat.
Fat-Butt in a pan (Brownies), Fat-Butt in a bag (Chips), Fat-Butt in a Bucket (KFC) Fat-Butt in a flat box (Pizza), and Fat-Ass-In-A-Glass (Margarita) etc.
"Pass me another slice of that Fat-Butt. Wow, this is the best Fat-Butt I've had in a long time! No one makes Fat-Butt better than your Mom!"