A girl with vagina lips that hang down, or a girl that sleeps with a lot of guys and has developed droopy vagina lips from sleeping around so much. The hanging V resembles the split in a mermaids tail.
One whose lips flap constantly. Perhaps flapping in the wind. Perhaps flapping in the sun. One necessary fact is everything that comes out of Flappy Lips mouth is more false than the result of a pregnancy test taken by a man.