First main use is in the song Molly whompin' which was on the mixtape 2800 by that artist stunnaman.
Not to be confused with the term molly whomp which has a dual meaning:
1: a cock slap
2: a gang beat down that has not happened yet or is being planned.
i molly whomped lisa last night and these guys came out of no where and started molly whompin on me