A shaggy dog story is a very long and silly story that usually goes nowhere and has a very disappointing ending. Imagine your parents telling you a story about a dog that takes a very long time to tell and gets more and more ridiculous as it goes on. You listen patiently, eagerly waiting for the ending, but when you finally get to the end, it's just a big letdown because nothing really happens or it's not funny. That's what a shaggy dog story is. It's a long and winding story that doesn't really have any point or purpose other than to waste your time and make you disappointed at the end.