Something you say when someone is boasting/threatening you and is acting like a bastard. It can also be used as a joke. It's pretty rude, and is also a quote from Austin Powers, so you can follow it up with something really dumb to say and everyone will think you're REAL funny.
The antonym of "brown bagger", A potato bagger is a girl that has a nice face, but an unattractive body. A potato bag race involves pulling a potato bag over the majority of your body while trying to hop to a finish line. From this game, evolved the name "Potato Bagger". It suggests that a girl with an unattractive body but a decent face should consider wearing a potato bag over her body while only revealing her face.