A defining point in any business, relationship or other human engagement in which a peer or superior behaves in a way that eliminates any traces of his/her credibility and, consequently, any sense of purpose in continuing the overall engagement.
"Things haven't been looking rosy for the company lately, but the boss totally jump the shark when he said 'no big deal' after half the best employees quit on the same day. I gotta get a new job - quick."
The precise moment when you know a program, band, actor, politician, or other public figure has taken a turn for the worse, gone downhill, become irreversibly bad, is unredeemable, etc.; the moment you realize decay has set in.
Tom Cruise jumped the shark the moment he jumped Oprah's couch.
Original meaning was the point when a television series shows it has run out of ideas and must resort to stunts to retain viewer interest. Derived from a scene in the last years of Happy Days when the Fonz waterskied over a shark. Includes actions such as "it was all a dream" episodes, live episodes, lead actors playing guest characters, and putting entire cast into a parody of some pop cultural event.
It looks like "Will and Grace" decided to jump the shark. They are doing a live episode in black and white where they are all characters from Star Wars. Elton John will play Jabba the Hut who shoots Jack with a "straight ray" gun.
The beginning of the end. Something is said to have "jumped the shark" when it has reached its peak and begun a downhill slide to mediocrity or oblivion. It's said to have been coined by Jon Hein, who has a web site, jumptheshark.com, and now a book detailing examples, especially as applied to TV shows. It supposedly refers to an episode of the TV show "Happy Days" in which Fonzie jumps over a shark on water skis, which Hein believes was the point at which the series had lost its touch and was beginning to grasp at straws.
A TV show's sure "jump-the-shark" sign: the appearance of a "special guest star".