shaggy-dog
adjective
shag·gy-dog ˌsha-gē-ˈdȯg 
: of, relating to, or being a long-drawn-out circumstantial story concerning an inconsequential happening that impresses the teller as humorous or interesting but the hearer as boring and pointless
also : of, relating to, or being a similar humorous story whose humor lies in the pointlessness or irrelevance of the plot or punch line
a shaggy-dog comedy
Did you know?
The origin of the adjective shaggy-dog isn't truly known, but lexicographer Eric Partridge rather believably tells us that it originated with a shaggy-dog story of the amusing sort that involves—of course!—a shaggy dog. Today, the word sometimes refers to a rambling story that impresses the teller as humorous or interesting but the hearer as boring and pointless, but it can also refer to a similar story (or movie or TV show) that is actually humorous and whose humor lies in its very pointlessness or irrelevance.
Word History
First Known Use
1946, in the meaning defined above