The (usually) surreptitious action of savoring the pheremone laden evidence of digital exploration of that magical female orifice. Commonly discovered by young men driving home after a date involving second base. Enjoyable at any age. Often characterized as a game.
“Frankie had himself a good game of stinkfinger all the way home from his date with new girlfriend.”
The aroma left upon one's fingers after insertion into a woman's vagina during sex; implies lack of proper hygene, not on the part of the person achieving "stink finger," but on the part of the woman involved.
I had sex with Vicky last night and left with an amazingly pungent case of stink finger.