There is a phrase from the world of TV – ‘Jumping the shark’.  It’s used when a TV series has an episode in which something truly ridiculous happens, something totally outrageous that defies the internal logic of the series. The term is believed to originate within an episode of the 1970s TV series ‘Happy Days’ when the main character, ‘The Fonz’ appears in a scene where he literally jumps over a shark whilst water-ski-ing.  the phrase entered in to the entertainment lexicon and stuck there