When you are about to go down on a girl and you start flapping her vagina lips with your hands. Hence, a HAND flap.
Boy: "Are you ready for this babygirl?"
Girl: "What.. WHAT ARE YOU DOING?"
Boy: "I'm hand flapping you babe."
Girl: "What.. WHAT ARE YOU DOING?"
Boy: "I'm hand flapping you babe."
by Maaashaa February 09, 2015