several definitions on Urban dictionary but this one seems to fit the usage:
Jew Bag: A person that has past the douchebaggery stage of being a ‘jew’ and has now reached the jewbag stage.
A person who is so full of jewishness that they may as well just be a jew bag full of jew.
Okay; I’m still re-reading “...past the douchebaggery stage of being a jew...”, and trying to figure that one out. LOL.