The muscle inside the vagina (cunt).
This was used as an insult in the HBO hit series Entourage where
character Ari Gold (played by
Jeremy Piven) told character "E" that he was a cunt muscle for waking his family up
in the early morning.
E: looks like i woke u up this time huh Ari?
Ari: Noo but u did wake my wife and kids
dick head, Vinnie better be sitting in prison with a DUI or
something is he?
E: No.
Ari: Then
what the fuck do u want Cunt Muscle!?