Someone who acts hard and presents an aggressive personality, but is in actuality just a big misunderstood softy who doesn't know how or has never had a real opportunity to show their kind side. Often has a reputation for bad behavior that doesn't actually have any proof to back it up.
Someone who is/was a nice person but due to social pressure and/or living in a rough area has adopted the personality of a twat just to survive.
(Rare) A homosexual burglar/thief/conman/criminal.
A: Shit! Gavin ticked me on 3 kilos and I've spent the money to pay him back! He's gonna hurt me bad!
B: That won't happen.
B: He's a Fluffian..
A: A what?
B: He acts hard so people don't rip him off, it's all a front, he won't beat you.
A: Phew, that's a relief!
B: He might bumlove you and make you felch him though...... He's REALLY gay you know, he just keeps it secret.
B: You're gonna have a ringpiece like a broken bagel when he's done with you, Ha!