skin box
A vagina or a belly button
He stuck his finger in her skin box
B.F Skin-her box
like the B.F Skinner Box experiments except with shaved pussies.
I made $500 because i signed my wife up for the B.F Skin-her box experiments, and now she done gone and have a shaved old puss
skin in the box
when you tuck the labia on an 'outy' vagina inside the hole, hence creating the 'skin in the box'.
"damn, that chick had an outy, but i gave her a 'skin in the box' and fixed that."