An extremely long-winded story that involves an excruciatingly detailed build-up leading, eventually, to a punchline that is only ‘funny’ as a practical joke where the listener has been tricked into paying close attention to a long, pointless story.
Shaggy dog stories play upon the listener’s preconceptions of joke-telling. The audience listens with certain expectations, which are not met or met in some entirely unexpected manner. A shaggy dog story derives its humor from the fact that the joke-teller held the attention of the listeners for a long time (as much as five minutes or more) for no reason at all, as the end resolution is essentially meaningless.
The phrase is likely American and first appears in print in Esquire magazine, May 1937. It may have originated with Albert Payson Terhune, a celebrated American author of animal stories, in particular, dog stories. His best known character was Lad, featured in several books and a film.
The Manitoba Free Press (a Canadian paper) printed, on November 6, 1926, a piece by Terhune, which appeared to be the true account of a dog named Lad, described as a ‘shaggy dog.’ The story was meandering and full of unnecessary details, and claimed that the dog survived shooting, clubbing, and burial and came bounding back for more.
William and Mary Morris in The Morris Dictionary of Word and Phrase Origins, say that the archetypical shaggy dog story involves an advertisement placed in the Times announcing a search for a shaggy dog. The advertiser is organizing a competition to find the shaggiest dog in the world, and after a lengthy exposition of the search for such a dog, a winner is presented to the aristocratic instigator of the competition, who says, “I don’t think he’s so shaggy.”
A typical shaggy dog story occurs in Mark Twain’s book about his travels west, Roughing It. Twain’s friends encourage him to go find a man called Jim Blaine when he is properly drunk, and ask him to tell ‘the story about his grandfather’s old ram.’ Twain finally finds Blaine, an old silver miner, who sets out to tell the tale to Twain and his friends.
Blaine starts out with the ram and goes on for four mostly dull but occasionally hilarious unparagraphed pages. Along the way, he tells many stories, only vaguely connected, and none of which has to do with the old ram. These stories include a tale of boiled missionaries; of a lady who borrows a false eye, a peg leg, and the wig of a coffin-salesman’s wife; and a final tale of a man who gets caught in machinery at a carpet factory and whose widow bought the carpet that had his remains woven into it. As Blaine tells of the carpet man’s funeral, he begins to fall asleep, and Twain, looking around, sees his friends ‘suffocating with suppressed laughter.’
They now tell him that at a certain stage of drunkenness, nothing could keep Blaine from telling about the wonderful adventure which he had once had with his grandfather’s old ram — and the mention of the ram in the first sentence was as far as he ever got with that animal.
Humans love to tell stories, and I would guess the tale is much older than the name and may have been a feature of fireside tales ever since fire was discovered. And there are always people around — you may have met one or two — who have no idea that a story is more — and less! — than just the excruciating details of what they did last week.
In the world of writing, the twist of explaining an exceedingly improbable plot line with “it was only a dream” is a classic ‘shaggy dog’ gambit, and highly unappreciated by editors everywhere.