1) Double bagging - the act of putting on 2 condoms before having sex, because a girl is so dirty that you are worried about catching something
e.g. "Urgh, that girl I banged last night was such a sket, I had to double-bag!"
2) Double bagging - the act of putting a bag over your own head as well as her head before sex, to prevent you accidently seeing how ugly she is
e.g. "You're so ugly, you're what we call a double-bagger. That means that I need to put a bag over my own head, just in case the one on your head breaks!"
3) A bike - a slutty girl who fucks around a lot
e.g. "She's such a whore, she's like the village bike. Everyone's had a ride!"