The World of Poo
Terry Pratchett
A joke that goes on too long
In Snuff (novel 39 of Terry Pratchett's Discworld series), Sam Vimes reads his son ("Young Sam") a book called The World of Poo. Young Sam is fascinated, especially when he gets to meet the author Felicity Beedle, who is also the author of such children's classics as Wee, Melvin and the Enormous Boil, Geoffrey and the Magic Pillow Case, The Little Duckling Who Thought He Was an Elephant. Miss Beedle is an important character in Snuff. And of course it is an accurate observation that boys are often fascinated by wee, poo, pus, etc.
So then Pratchett took the joke to its extreme, and wrote the book ostensibly written by Miss Beedle, The World of Poo. It's a rather substantial work: two hours in audio, so novella length. It's too much. It's not a bad joke, but by the time you listened to two hours of it, the joke has gotten very, very old.