By which I don’t mean TV-program-that-is-a-work-of-fiction–I mean a TV program that was fictionalized within another TV show or movie.
Off the top of my head, I have to give the TV-division award to The Itchy & Scratchy Show. They fight! They fight! They fight and fight and fight! Is there any show-within-a-show that better captures mindless id-level TV in its essence? (And isn’t it somehow touching that the above-embedded YouTube clip of Itchy and Scratchy killing Hitler was posted in German?)
In the movie division, you’ve got a rich history to choose from–the eponymous program of The Truman Show, the roster from the movie Network. But simply on the basis of title alone, I have to give it to Mike Judge’s creation from Idiocracy: Ow! My Balls! (For the rationale for which, see Itchy & Scratchy, above.)
I’m sure I’ll kick myself repeatedly as you mention shows I’ve completely forgotten about, so have at it, and let the self-kicking begin!