A "bagger" is a term for someone who is below par on the attractive scale, so below you have to put a bag over their head.
A "double-bagger" is someone so hideous, you have to put a bag not only over their head, but your own.
"I heard you had sex with that really nasty skank who's always at the bars on Mondays."
"Yeah, I was so wasted,she was a complete double-bagger."
First Defintion: When someone wears underwear and then turns them inside out and wears them the next day.
Second Definition: Imagine one sitting taking a shit, he thinks he's done, reaches for the toilet paper and then has another full shitting session. A double deuce!
"Why is there a skidmark on the outside of your panties?" You double deucer!