The sound of a book being slammed shut is a great way for a character who just had their nose buried in it make it clear that they mean business (or sometimes, they've realized something else does). Being a relatively quick and loud gesture makes it the perfect way to interrupt the more passive action of reading (or writing, or drawing, or dictating or whatever the would-be literate was doing before they were so rudely interrupted). A character who wasn't that engrossed might still close a book they had open nearby as a sort of pre-battle taunt.
If a character's being distracted or otherwise harassed while they're reading, calmly but loudly clapping the book shut usually indicates that they've had enough. Teachers have a specific variation, where they'll snap a book they're reading from shut to get the attention of an inattentive pupil. Another variant has the character casually holding a book in an open palm (using the other hand to turn pages or follow the text with their finger) and quickly closing it and stowing it one-handed (often after pulling it out in some dangerous situation).
The Badass Bookworm and Warrior Poet like using this as an Ass-Kicking Pose (especially the one-handed version with the latter, since reading a book mid-battle makes for a good source of Dissonant Serenity). The more scholarly sort of wizard is more likely to use the "taunt" variation (in the same way a more martially minded warrior might brandish a sword). For other characters with books, the chance of it happening is inversely proportional to how often a given character reads. If a Book Dumb warrior ends up forced to read, it's almost a given they'll dramatically slam it shut (and possibly brain someone with it) as soon as the opportunity presents itself.
- In Soul Eater, Maka's "Maka Chop" is whacking the object of her ire over the head with a book. If she's reading a book at the time, she typically snaps it shut before beginning to say "Maaaaaakaaaa...".
- In the Ghost in the Shell: Stand Alone Complex episode "IDOLATOR", a bystander reading a book does this after he spots plainclothes officers approaching a suite where a Yakuza is having a meeting with Jarti (a revolutionary who Section 9 are following more subtly). Needless to say, it turns out he's a combat android they'd left as a guard, who whips out a machine pistol and starts a shootout.
- In the manga of Battle Royale, a flashback shows Kiriyama snapping his book shut and shouting "Some of us are trying to study!" when a few hoodlums try to start a fight in the library. He then opens a can of whoop-ass.
- In Roland Hedley's first appearance in Doonesbury, Walden's commune residents give him outlandish BS for a report on youth trends. When Zonker and Mike avow "We give you our word of honor we represent a national trend." he snaps his reporter's notebook shut and takes their word for it.
- In The Famous Five Five Go Adventuring Again, Mr Roland the tutor does this after a revelation of a serious incident during the children's lessons.
Mr Roland shut the books on the table with a snap. "We can't do any more lessons this morning," he said.
- In Harry Potter and the Chamber of Secrets, Hermione slams the book Moste Potente Potions shut when Harry and Ron express their reservations about their highly daring act of making Polyjuice Potion.
- In Harry Potter and the Prisoner of Azkaban, Hermione does this and storms off to another class when Ron makes an Innocently Insensitive remark. This leaves Harry and Ron confused, since they don't know she's using a time turner to attend multiple classes.
- In The Worst Witch, Miss Cackle the headmistress slams a register shut when Mildred appears in her office, perhaps knowing that Mildred is about to confess to something dreadful, as indeed she does.
Miss Cackle slammed the register shut and pushed her glasses on to the top of her head."Now, Mildred, what can I do for you?"
- Played for Laughs in Black Books when an over-caffeinated Manny mistakes this for a gunshot and tackles Bernard to the ground.
- Doctor Who: In "Day of the Doctor", after Clara motorbikes her way into the TARDIS while the Doctor is reading Advanced Quantum Mechanics, he snaps the book shut. "Fancy a week in ancient Mesopotamia followed by future Mars?"
- Happens on Gilligan's Island in the episode where the castaways ate the radioactive vegetables. The Professor had his nose buried in a book, trying to determine what they should do, while the Skipper and Gilligan laid in their hammocks. The Professor asked out loud how he could have been so stupid, then slammed the book shut and announced, "Lying still could kill us! We need to be up moving around!"
- Star Trek: The Next Generation:
- In the episode "Samaritan Snare", Picard and Wesley are taking a long shuttlecraft ride to a Starbase. At one point Picard does it in annoyance at all the questions Wesley is bothering him with.
- In "Elementary, Dear Data", Data and Geordi are playing Holmes and Watson in the holodeck. Geordi records Data/Holmes in Watson's journal...and slams it shut in frustration as he realizes Data is just reciting an existing Holmes story instead of actually deducing clues.
- In the episode "Captain's Holiday", Picard does this upon being harassed by a Ferengi while trying to relax on vacation.
- Ellery Queen: In the two-hour pilot "Too Many Suspects", Ellery does it when a girl he agreed to watch for her parents gets upset at his continually having his nose in a mystery book and tells him who the murderer is.
- Devious Maids: Marisol does this to Damian as a way to indicate that she has had enough of their playful yet dramatic banter.
Damian: What kind of maid uses the word "inquisitive"?Marisol: The kind who can read. (snaps book in his face)
- In the music video for The Word Alive's "Rise", Faker does one of these after he looks up to see Ambition. The book releases a small amount of arcane energy when slammed shut.
- The opening cinematic for World of Warcraft's Burning Legion expansion featured a Draenei picking up a magic tome before doing this and setting off.
- Super Smash Bros. Wii U/3DS: Robin's intro trailer has him doing this with a wind tome right after using it to drive Captain Falcon back from attacking Lucina.
- Atlantis: The Lost Empire: Milo has just been handed the Shepherd's Journal, a supposed first-person account of the lost city of Atlantis, by Mr. Whitmore. As he peruses it, Whitmore comments that it's probably fake. Milo quickly shuts the journal and tells him that he is certain of the existence of Atlantis and is willing to do anything to prove it...which is exactly what Whitmore wanted to hear.
- In Mickey's Christmas Carol, Scrooge is working on his ledger when Donald Duck (as Fred) comes in and wishes him a Merry Christmas. Scrooge slams the ledger shut and asks him "What's so merry about it?"
- Some traditions in Christian worship involve snapping the Bible shut, especially on Maundy Thursday, or Good Friday, symbolising the death of Christ.