shaggy-dog story is also applied to long-winded jokes (which are sure to be pointless, and may involve convoluted puns); Eric Partridge offered this (shortened) version of the original shaggy-dog story:

A grand householder in Park Lane, London, had the great misfortune to lose a very valuable and rather shaggy dog. He advertised repeatedly in The Times, but without luck, and finally he gave up hope. But an American in New York saw the advertisement, was touched by the man’s devotion, and took great trouble to seek out a dog that matched the specification in the advertisement and which he could bring over to London on his next business trip. He presented himself in due course at the owner’s impressive house, where he was received in the householder’s absence by an even more impressive butler, who glanced at the dog, bowed, winced almost imperceptibly and exclaimed, in a horror-stricken voice, “But not so shaggy as that, sir!”

-joe (shaggy) friday