When a piece of smoking hot gammon has a nice rack and rear, but not a face to match. The only way you would give her one, would be if you put a paper bag on her head so that you enjoy the benefits of her body, but you can imagine she is someone else. Hence; she is a Paper Bag Shag.

A person with an outwardly dominant, masculine, or aggressive personality, but who also enthusiastically takes on the submissive or "bottom" role in the bedroom.