Jump the shark
1. (idiomatic, of a television program or other narrative) To resort to using an obvious or unbelievable gimmick in a scene, episode, or storyline as a means of maintaining viewership, especially when the show’s quality and/or popularity has begun to decline. The phrase alludes to the sitcom Happy Days, in which the character Fonzie (Henry Winkler) jumps over a shark on water-skis in the fifth season.
This show used to have some of the wittiest writing in television, but they really jumped the shark when they introduced a contrived alien invasion in the seventh season.
2. (idiomatic, by extension) To signal, especially through a conspicuous activity, event, or maneuver, a decline in the progress or evolution of something (e.g., a company, a brand, a political endeavor, etc.).
The global tech giant, whose smartphone brand transformed the everyday technological landscape, seems to have jumped the shark this week when they revealed a line of computer-synced sneakers touted as their new flagship product.
The governor was accused of jumping the shark during his re-election campaign by joining in with the cheerleading squad at his former high school’s football game.