story (of a … or joke which is long-winded, often filled with irrelevant details, and ultimately dull or boring) adj. shaggy dog

The movie “Ray” by Taylor Hackford is at heart a shaggy dog story, long, pointless, inconsequential and filled with odd details. (Michael O’Sullivan, “’The Comedian’ Shows a Comic Who Doesn’t Know When to Stop,” The Washington Post, 2/3/2017.)

This word can be synonymous with boring, rambling, pointless, or long-winded when referring to a story or joke which is filled with irrelevant details, and ultimately dull or boring. It can also describe a joke of that variety.