Poppins Box is a term to describe female genitalia. This term makes reference to the movie Mary Poppins who carries around a bag of infinite internal proportions. She is seen removing an entire coat rack amongst other large items from her bag.
This definition is etremely useful when referring to a woman with a seemingly large, deep, or otherwise spacious vagina.
My dick's so big, this bitch better have one hell of a Poppins Box.
I was double fisting her Poppins Box up to the elbows.
Man,lets just say that her Poppins Box is so dirty, that you will need a spoon full of sugar to help you go down.