A Raff is a common term in London used to describe a person who spends more time sleeping around than making sammiches. Raffs are prone to many of the same difficulties as whores, namely STDs and threats of pwnage from angry cheated-on girlfriends. She is a raff until she sleeps with you. A "raff" who does sleep with you is no longer a raff, but a "cool chick" who knows how to have a good time. Then, when you get tired of her and it's time to move on, she goes back to being a raff again. If she looks like she's trying to shoplift week old cold cuts in her panties, she's probably a raff.
Person A: "That raff is like a merry-go-round; everybody got a turn."
Person B: "I hear a raff is like a sausage in a wind tunnel"
"And the legend of the raff was way hardcore!" Jack Black on raffs
"Exactly! Only a raff would want to be with a douche like me!" Danny Franklin on raffs