A Greebo is essentially anybody who is not a Scallie
They can be a skater, or a punk or can have long hair and baggy trousers. It doesnt matter who they are, if they don't have a nike t-shirt or a cheap gold ring, they are classed as a "Greebo"
"Scallie" Oi Greebo, pull you're trousers up and gimme your wallet.
"Greebo" Fuck you