Someone with an ugly face but hot body; a paper bag over the head would render them infinitely more sexually attractive.
Amy: Is Katy's new boyfriend hot?
Rachel: He works out a lot but he has acne and crooked teeth. He's a total Paper Bagger.
A girl who the only way you'd have sex with them is if they wore a paper bag on their head. See also one bagger, two bagger, or three bagger
Cohort A: That girl has a nice body, but what a nasty face
Cohort B: Yep, definitely a paper bagger.