You Can't Do That On Television was a show on Nickelodeon in the 1980s, and one of the most popular Nick shows of its day. It set the stage for Nick's famous messy theme, especially introducing Nick's famous slime (in multiple colors). On the show, if someone said "I don't know." while on camera, they would get slimed.
The intro to the show was heavily influenced by Monty Python's Flying Circus.
Trivia
Popular internet reviewer Nostalgia Critic reviewed the show as a part of his Nickcoms episode during "Nickelodeon Month". He commented that the show's name is contradictory, as they are in fact doing everything on television.