A literary example occurs in Red Dwarf: Infinity Welcomes Careful Drivers: a scene in which a depressed Lister remembers how he arrived on Mimas is frequently interrupted by two pimps arguing over a girl called Sandra. This argument involves two ears being cut off and the death of both participants.
One The Knowledge book dealing with magic tricks had plenty, based around the antics of the magician's bumbling assistant Clumsini. Perhaps the best was him hiding to avoid a squad of angry cats.
The Pumpkin Soup series of children's picture books by Helen Cooper (Pumpkin Soup; A Pipkin of Pepper; and Delicious) all have a wide variety of amusing background details in the illustrations. In Delicious, the activities of the insects practically qualify as an additional story.
A scary version in The Curious Incident Of The Dog In The Nighttime. Christopher, who is autistic, is focused on retrieving something he dropped on the train tracks. The text is almost all about his efforts, and gives only a few mentions to the consternation of the crowd, and the brightening light and growing rumble of what the reader (but not Chris) recognizes as an approaching train.
In Percy Jackson and the Olympians: The Battle of the Labyrinth, the campers are holding an emergency meeting about the search for Daedalus's workshop in Camp Half-Blood's fencing arena, while Quintus's pet hellhound Mrs. O'Leary is chewing on a fencing dummy.
Many, many of them can be seen in the children's picture book Mrs. Watson Wants Your Teeth:
When the book's protagonist, a nameless young girl starting first grade, is getting on the bus, her cat is standing on its hind legs and waving to her along with her dad.
In the same scene, a kid is hanging upside down from the ceiling of the bus.
While our heroine is listening to a second-grader scaring her with rumors about her new teacher (which takes up a few pages), a boy can be seen annoying the girl he's sitting next to, who proceeds to tape his mouth shut and his arms and legs together.
As our heroine and the second-grader get off the bus, a kid in pajamas and bunny slippers walks out behind them and the kid from before is still hanging upside down from the ceiling.
On the following page, which takes place in the school hallway, a girl opens her backpack to find a puppy in it.
On the second-to-last page, everyone is back on the bus, the unnamed boy is being annoying again, and the girl is taking out her roll of duct tape. Also, there's a kid behind the bus running to catch up.
The less serious nonfiction computer books sometimes might contain interesting or funny stuff used as examples or in the screenshots. For example, Elizabeth Castro's HTML 4 for the World Wide Web: if you pay attention to the text used in examples, you'll not only learn HTML, but also get to know every single bit of trivia about Elizabeth's four cats.
In The Wheel of Time, Egwene is reflecting on an earlier conversation, and comments on a specific remark aloud, saying, "That's a bucket of horse spit." A man in the background carrying a bucket responds by staring at her in surprise and amazement.
In Why We Took the Car, while the policemen talk to Maik at the police station, one policeman is trying to get the coffee machine to work with any possible way...except for plugging in the power cord.
The zombie parody How to Survive a Zombie Apocalypse has instances of this when a member of a survivor group gleefully philosophizes about life while her partners are getting mauled by zombies behind her.
In almost every Charms class, while the Trio are discussing important information, Professor Flitwick is having all manner of unfortunate things happen to him (usually courtesy of Neville).
In Harry Potter and the Order of the Phoenix, the trio's discussion on their current situation takes place in a crowded hall where Peeves the Poltergeist is shooting ink pellets at people. He subsequently gets into a fight with another student and the scene ends with him emptying an entire ink bottle over the girl's head, all without affecting the main course of the scene.
In the Jeeves and Wooster book The Code of the Woosters, Sir Watkyn Basset and Roderick Spode accuse Bertie of stealing, when Madeline Basset turns up and objects to the accusations. She doesn't speak again until three pages later, when Bertie notes she had been silent up to that point due to the fact that she had inhaled an insect and been busy choking on it in the background up until that point.
In Atharon , during a rather tense scene a character drops her bow in anger. Her servant refuses to give it back to her until she calms down. The event is ignored by everyone else present.