Irritating little green alien

From BackYardWiki

For some reason, the makers of otherwise-excellent '60s Hanna-Barbera cartoon The Flintstones decided halfway through the final season to introduce the Great Gazoo. For those fortunate enough not to remember him, Gazoo was an irritating little green alien who did three things:

1. Constantly referred to Fred and Barney as 'dum-dums';
2. Caused endless trouble for our hapless heroes, often getting Fred into trouble with his beloved Wilma;
3. Made the viewer want to smash the television screen with a mallet in response to sheer, mind-bending awfulness.

Thankfully the series ended not too long after Gazoo's appearance (so, in effect, we can blame him for having KILLED THE FLINTSTONES) and is generally cited, by those people who cite such things, as the moment when the show jumped the shark.