Short for "Well, what you gonna do about it".
A backstabber, lowest of the low, a mofo who would sell his house for the chance to grind your face in the dirt.
Lazy version of "What the hell?" or more commonly, "What are you talking about?"
Used to convey irritation, confusion, or just when you don't have a better word popping into your head.
Person #1: Have an oatmeal grape orange peelcookie!
Person #2: Whazell?