When the bitch your fucking is so ugly you can't even look her in the face, so you put a paper bag over her head. When you finish, you splooge all over the bag. Then proceed to punch and break her nose through the convenient hole you have cutout in the paper bag (she thinks its so she can breathe, you know its so you can punch her afterwards)...leaving you with a red paper bag
Bonus: Leave a cutout for her eyes so she can see your fist coming at her big ugly face.
David: So did ya fuck Dana last night?
Mike: Yeah man, that bitch was so ugly, I ended up having to give her a red paper bag!