2) When a man brings his female lover to such a state of arousal, that her vaginal canal produces a surplus of the lubrication required to facilitate intercourse. The male then proceeds to penetrate his partner so vigorously that her labial folds begin to "flop."
Note: Especially popular with women from the greater Pittsburgh area. Traditionally, the female would wear a small pair of furry booties on her feet while engaged in the aforementioned act.
Nicole: Boi, why you all about moppin', let's get to lippy flopping!