Bugs Bunny's catchphrase, usually said right upon meeting a foe, while snacking on a carrot. But why "Doc?" According to sources, "What's up 'Shirley'" just didn't sound good. His first utterance of the words can be linked back to his early days in showbiz, as highlighted in the cartoon "What's Up, Doc?"
After many years in a truly repetetive chorus line, Bugs joined already famous entertainer Elmer Fudd, after Elmer spotted him amongst the poorer entertainers. Bugs and Elmer's routine would involve Elmer telling jokes to Bugs, who was dressed in a ridiculous "pinhead" costume, and then further humiliating him by telling him the punchline, accompanied by a pie or seltzer in the face. When the show reached NYC, Bugs decided to turn the tables by telling the punchline instead of Elmer, and then humiliating HIM. Elmer responded to this with a shotgun in Bugs' mouth, to which Bugs nervously uttered, "Eh..what's up, Doc?" The audience went wild, and Bugs was offered a picture deal.
On rare occasions, Bugs has been known to say other names besides Doc, such as "dogs" to a pack of vicious dogs, or "beaverpuss" to a particularly hairy-bearded Arab.