fattyfattyboomboom Share definition Flag a slang and careless word often used when in a state of arousal or lame sarcasm Derek, "Oh Martha your breasts are fattyfattyboomboom (orgamsm) Enrique, "Hahaha fattyfattyboomboom!" (Piss pants) fattyfattyboomboom by rawk god January 13, 2007 Get the fattyfattyboomboom mug.