Doctor Who star David Tennant played himself (and the Doctor) in the final episode of Extras, and dredged up every painful stereotype about the show. It's all there: the crappy costume, the technobabble, the dumb science lesson (sodium chloride=salt) and the dying alien's mouth goo. It's not nearly as good a Who spoof as the French and Saunders version or Curse of the Fatal Death. But it's worth a look for David Tennant mocking his own jutting-jaw acting.