from Wiktionary, Creative Commons Attribution/Share-Alike License
- v. To undergo a storyline development which heralds a fundamental and generally disappointing change in direction.
- v. To experience a decline in quality, appeal, popularity, etc.
From "Hollywood (Part 3)", a 1977 episode of the TV series Happy Days, in which the character Fonzie jumped over a shark on waterskis, after which (supposedly) the show bore no similarity to its original form. (Wiktionary)