Biffing Plate 

The small area of skin between a woman's cunt and asshole where a guy's balls slap against when he is fucking her

Boy, Mary's biffing plate got a good hammering last night

Biffing Plate by sanddevil March 14, 2009

biffing plate 

The area of a chick's ass that a male's Jackson Pollocks hit off when he bangs her

I sat down on my sandwich.
Now it's flatter than Jenna's biffing plate.

biffing plate by Theeph May 28, 2003