Origin of shaggy dog (story)as if from such an anecdote involving a shaggy dog
shaggy dog (story)shag·gy-dog story
(plural shaggy dog stories)
Uncertain; prob. from one of two jokes, one in which a protracted search for an alleged remarkably shaggy, talking dog ends in the discovery of the dog which, though it can indeed talk, is disappointingly not so shaggy after all; or one in which an even more protracted search for the shaggiest dog in the world ends in the utterly anticlimactic punchline "Now that's a shaggy dog!".