It's the girl version of T-bag. A girl is up above the face of someone else & she would dip down and rub her vagina across their forehead then leave a snail trail.
"If you don't shut your mouth, I'll shut it with my vagina" ... clamstamp.
Clam Stamping is when you don’t see in the middle of the night and sit on your toilet only to find out the cover was on it, leaving a lil bit of clam juice on your seat cover
Jennifer: hey girl, your seat cover has some crustier on it, looks suspiciously vaginal shaped?
Bonnie: oh yeah, last night I went to take a piss and accidentally sat on the seat COVER and not to seat
Jennifer: oh shit! You gave the seat cover a good clam stamping!
the feminine verson of tea-bagging. For a female to press her virgina upon a person or object in the same manner a male would drop his genitials on what he was tea-bagging.
In retalitation of Dr.Phill tea-bagging Opra during the people's choice awards, Ms. Winfrey slipped Dr Phil a Ruffitini and proceeded to Clamstamp him while at a book signing.
When a woman acts as if she is going to perform oral sex while her partner is horizontal, and she instead frog-jumps to place her vagina on the partner’s face.