When a TV show, movie, or band has reached a point where their own absurdity can no longer save them from themselves and they would be best served by being put out to pasture, they are said to have "jumped the shark." This term is derived from an episode of Happy Days where the Fonz jumped over a shark on waterskis (the Fonz was on the skis, not the shark) and the show is thought to have gone down hill afterward.
Thanks to the glory of the internet, this idea flourished and was explored in depth and supported by a website, www.jumptheshark.com (please note that I did not actually link this site). On it, one could look up their favorite (or least favorite) show and could submit their ideas for exactly when a particular show had jumped, or vote on some of the most popular choices. This website actually developed a pretty strong following and the term "jump the shark" reached fairly widespread use. However, it would seem that sometime in 2006 the creator of the site sold it to Gemstar, the parent company of TV Guide, who in early 2009, scrapped the original site and basically turned it into a portal to TV Guide's website. In an irony to end all ironies, the Jump the Shark website essentially jumped the shark.
While I had been familiar with the old website, I didn't discover its fate until a couple of months ago when I was looking to see when a particular show had jumped. I was pretty dismayed at seeing what had happened, but fortunately Wikipedia pointed me in the direction of the spiritual successor of the original website, Bone The Fish.
Bone The Fish has essentially recreated the old site, and seems to have expanded on the number of categories. On the site you can read a more detailed account of what happened to "the site that shall never be named" while posting your thoughts on, say, when Friends started to go down hill (Ross and Rachel break up again??). While I'm not sure if the term "boning the fish" will ever gain the same acceptance as "jump the shark," this is definitely a website I would suggest taking a look at.