When a man is receiving fellatio from an individual and he elevates one of his legs, either over the shoulder, up on the bed, desk, countertop, etc; he is left on one leg, like a flamingo. While up on one leg, the woman takes and "sweeps" the male's leg by kicking it out from under him. NOTE: The leg he is balanced on must be swept or pulled forward (or sideways)/towards the giver. If she kicks it backwards, the man will fall forward. By "sweeping" or pulling the leg towards her/back to front, he will fall backwards.
Although this can pertain to male/male or female/female interactions, this was defined for the male/female interaction where the female is the giver.
This has a double meaning because flamingo is also a slutty girl.