Robot Chicken is a popular "sketch comedy" show. It's entirely stop-animated with various action figure style characters. 12 year olds generally find it hilarious. Oh, and it also won an Emmy.
Every episode of Robot Chicken has no less than two celebrities, generally many more. You probably haven't heard of all of them, but trust me they're famous.
One might think that celebrity guest stars would voice themselves. They generally don't on Robot Chicken, and when they do it's in incredibly self-depricating rolls (ahem-Ryan Secrest)
If you haven't watched every ad or movie in existence, you probably won't understand everything on Robot Chicken. Who the hell has seen Sleepaway Camp, or whatever it's called (clearly I haven't seen it.)
The show also enjoys mixing random shit and showing the result. Scooby Doo and Jason Voorhees? Why the hell not! Throwing zombies, cereal mascots, and Ryan Seacrest together in an American Idol parody? Sheer genius! He-Man and Michael Moore? OF COURSE! That's what the show is all about, and if you don't like it, go complain on a forum somewhere.