— jump the shark
: to undergo a significant change for the worse that decisively marks the point at which a period of success, excellence, or popularity ends (as for a TV series) and an unrecoverable period of decline begins
The phrase jump the shark derives from a 1977 episode of the American TV series “Happy Days” (1974–1984) in which the program's most popular character, Fonzie, jumped over a shark while waterskiing in his trademark leather jacket. Some years later that episode came to be widely identified as marking the beginning of the iconic show's decline.
<Nearly all TV shows ever produced have jumped the shark eventually. Such is the nature of television's creative conundrum. — Monica Collins, Boston Herald, 9 Jan. 2000>
<Most TV series take three seasons to jump the shark, but in the theater it can happen in 20 minutes … — Bob Verini, Daily Variety, 18 Sept. 2009>
<But in its headlong embrace of capitalism and corporate tie-ins, “Sex and the City” may have finally jumped the shark. — Laura Compton, San Francisco Chronicle, 30 May 2010>
<Not everyone agrees when Picasso's art jumped the shark. — Jeffry Cudlin, Washington Post, 27 Feb. 2011>