Watching TV the other night Family Guy was on, a good show I must say. But this one episode I was watching particularly got pretty annoying as it went on. It involved Peter singing and dancing throughout the episode to Surfin' Bird by the Trashmen. Now it was funny this first couple times he did it, but the joke was dragged probably on purpose.
Now Family Guy isn't the only show guilty of the one joke episode. South Park recently did an episode about Indiana Jones getting raped. And there one joke claim to fame is that you shouldn't shoot a guy in the dick as seen by Butters multiple times in the episode.
Now after analyzing these two successful cartoons that have been on the air for years now. There formula is quite simple, take one or two jokes build it around a narrative and stretch it to 22 mins.