shaggy dog story

Short definition from Wiktionary

Noun

1. 1
   An intentionally long-winded joke or tale featuring the narration of typically irrelevant details, and usually ending with an absurd or pointless punchline which is often a pun or Spoonerism on a known catchphrase, with the intended humor deriving from the combination of the excessive length and the anticlimax.
2. 2
   Alternative form of shaggy dog story.