Arse-flap Share definition Flag A loose flap of skin, hanging from a persons anal area. Sometimes In the appearance of a pouch that may flap if blown by the wind. Can be tied up with a a hair lackey. Avril Lavigne has the biggest arse-flap I've ever seen. I wonder how she cleans it! Arse-flap by Smythe November 1, 2003 0 0 Get merch Get the Arse-flap mug. Buy Now β $32.95 See more merch