jump the shark

Meanings

1. Of television program or other narrative, to undergo a storyline development which heralds a fundamental and generally disappointing change in direction.
2. To experience a decline in quality, appeal, popularity, etc.

Etymology

From Hollywood (Part 3), an episode in 1977 during the fifth season of the American television series Happy Days, in which the character Fonzie jumped over a shark on waterskis. The expression argues that it was at this point that the show bore no similarity to its original form.