There have been a lot of celebrities in WoW commercials and some of the modifications to the default character models are kind of cool, I was thinking it would be kind of neat to see them again in the form of raid bosses. I was thinking they could be fought similar to the way the Faction Champions in ToC played out, in that you would randomly face a team of celebrity characters. One run you might face a team of Ozzy, Chuck Norris and Verne Troyer, and the next time you might be set against Shatner, Jean-Claude Van Damme, and Mr. T.
I know that the Faction Champions fight received a mixed reception, but I found the fight enjoyable in that it was always a slightly different experience. This would be along the same vein, where each of these celebrities represents a different class, and they can incorporate some unique attacks that way (roundhouse kicks, mohawk grenades, shredding).
WoW has used joke bosses in the past, its a game that is constantly throwing pop culture references and making fun of itself. As far as where it could fit into lore, maybe all of these characters are a secret society and they're running the same raid that you are trying to stop some worldly threat and you clash. Its happened before.
Feel free to pick apart my idea, or else suggest bosses or encounter types that you'd like to see.