A gram of weed. Usually sold packed tightly in a tiny ziplock bag.
Party goer 1: Hey man how much weed did you buy?
Party goer 2: I bought a g banger just for myself.
When put your hand down your pants and starch around and inside your asshole so you can pull it out, to have a sniff and lick of your left overs down there.
My ass crack was real sweaty so I had a chocolate paddlepop to make sure it was okay down there.