1) Anticlimactic anecdote 
[TV] Shaggy Dog Story is a charity programme for Children in Need, put together by the BBC in 1999 as a sequel to the previous year`s Future Generations video (featuring children`s programmes), and the great success of 1997`s `Perfect Day` charity single. It was first shown on 27 December 1999. Shaggy Dog Story was dedicated to the BBC`s co... In its original sense, a shaggy dog story is an extremely long-winded anecdote characterized by extensive narration of typically irrelevant incidents and terminated by an anticlimax or a pointless punchline. Shaggy dog stories play upon the audience`s preconceptions of joke-telling. The audience listens to the story with certain expectations, whi....
[n] - a long rambling joke whose humor derives from its pointlessness
noun a long rambling joke whose humor derives from its pointlessness