1) A broad term, it can be used when describing or talking about a group of people who enjoy listening to cheese rock, music that is unworthy of being called music. Also, anyone who separates themselves from other people because they are "unique" even though they really aren't and play in shitty garbage bands and desperately need haircuts.
2) People who need to realize their lives are pointless unless they make drastic changes.
"Hey look at those Banger Changers!"
Guy 1: "Hey dude, have you spoken to your friend lately?"
Guy 2: "Noo...he's been a banger changer lately."