Very much Truth in Television, and something constantly warned about in the armed forces around the world, as you can never tell when the person on the street you are talking to might secretly be an espionage agent.
Because Technology Marches On, it's even easier than ever to get people killed by running your mouth off, thanks to websites such as LiveJournal, Facebook, TVTropes, and that other wiki. Always beware that when you talk about something that is privileged or secret, you might as well be standing on a roof top with a big sign and a megaphone.
A real danger, even if you don't live in a City of Spies, particularly if you unwittingly work near The Mole or are the target of a Honey Trap (a warning commonly given to members of the military when they are going out into town: "If a girl acts interested in you, and if you're ugly, then it's a trick.")
See Cannot Keep a Secret for characters who tend to do this all the time.
- In Naruto, a flashback to the night of the eponymous character's birth shows Kakashi talking to Rin's grave, wherein he talks about said information. Unbeknownst to him, Obito, who Kakashi believes to be dead, is eavesdropping, and learns the secret — after which he tries to kill Naruto, then unleashes the Kyubi.
- The Anthem of the Heart happens because Jun blames herself for her parents' divorce, which came about because she blabbed to her mom about seeing her dad commit adultery at a love hotel.
- In the One Piece Self-Insert Fic This Bites!:
- Inserted character Jeremiah Cross manages to keep his secret from the crew for a short while... up until he comes down with a case of Primal Cholera that, among other things, dissolves enough of his mental barriers to have him mention several things over the course of his few days of illness that were impossible for him to know. Once he's treated and finds that out in Chapter 12, his reaction is an immensely justified Oh, Crap!, but fortunately the crew forgives him after The Reveal two chapters later.
- Vivi's blurting of Crocodile's identity is Lampshaded by Cross when she asks to be let in the loop of Secret Keepers.
Cross: But pleeeeease promise me that you won't blab anything we need to keep secret to anyone who shouldn't know it?
Vivi: [facefault] T-that was one time!
- Who Framed Roger Rabbit has the main character asking a few too many people where the detective's office is, allowing the bad guys to figure out where he's going.
- Twice in The Little Mermaid:
- How Flounder inadvertently got Ariel into trouble with her father, King Triton, for going up to the surface.
- Let's just say that Sebastian and his big mouth certainly split the beans to King Triton who found out about Ariel's rescue for Eric and her grotto. Sebastian soon regrets his mistake afterwards.
- The SpongeBob SquarePants Movie: Plankton calls Squidward this for deciding to confront him upon finding out about his evil plan, then threatening to take it up to King Neptune. This allows Plankton to prevent Squidward from doing this by activating the bucket helmets he's given to the entire populace to turn them into his slaves, with his first order being to subject the Squid to the same fate.
- The Sum of All Fears movie has one nuclear scientist's mom giving away some information to Clark that allows him to find the terrorist's nuclear production area.
- Parodied in a flashback in Airplane!: The hero tells his girlfriend that he's going to be sent out on a mission soon. He then goes on to mention exactly where he's going, what he's going to be bombing, what time of day they'll be attacking, how high they'll be flying, and what direction they'll be coming in from. But he refuses to give her a rough estimate of when he'll be back from the mission, because that's classified.
- Briefly comes up in WarGames, after David and Jennifer find out they accidentally hacked into NORAD and almost caused A Nuclear Error. After Jennifer gives a speech about how they won't be suspected if they act normal:
Jennifer: Oh God, this is so unbelievable! Listen, do you think maybe I could call Michelle and tell her?
David: NO, JENNIFER, DON'T CALL HER!
Jennifer: Sorry. All right, I won't.
- Better Luck Tomorrow: Virgil is very chatty and has trouble keeping secrets. After he takes over as leader of their gang, the administration busts their test cheating ring because he went around the school bragging about it.
- In Shoot-Out at Medicine Bend, Nell gets Clegg drunk and causes him to blab all of his secrets: from the fact that he and his friends aren't really Brethren to the fact that King has a secret shipment coming into town.
- The Ballad of the King's Jest by Rudyard Kipling, about a talkative man running into the Great Game and discovering that his boss in Kabul doesn't have so much patience that this could end well for him.
- Harry Potter
- Rubeus Hagrid in Harry Potter and the Philosopher's Stone does this several times. Trust him with your life, but not your secrets. The movie version even gave him a Catch-Phrase relating to this: "I shouldn'ta told ya that!"
- Bertha Jorkins in Harry Potter and the Goblet of Fire is no better at keeping secrets than Hagrid. As Sirius says it once: "She was a bit dim, but she had an excellent memory for gossip. It used to get her into a lot of trouble; she never knew when to keep her mouth shut."
- Jim Hickman was spoken of as being this by Mac McCullum in the Left Behind book The Mark when he accidentally lets slip to Nicolae Carpathia sensitive information shared in confidence by Nicolae to his close associates in the Global Community top brass, which leads to Ramon Santiago's death and Jim's own suicide.
- Nina Tanleven: In The Ghost Wore Gray, Baltimore unwittingly shares the secret of Captain Grays diary with the villain of the book. He admits later that hes paid dearly for his mistake (the villain knocked him out and stole the diary).
- In Noob, Gaea had to stop playing her previous MMORPG because a friend of hers couldn't keep her mouth shut about the scams she was pulling on other players. That friend is playing her current MMORPG also, but Gaea's Manipulative Bastard habits where getting an embryonic Open Secret status by the time they ran into each other, making the info less sensitive.
- The undoing of more than one of Parker's carefully planned heists in the novels of Richard Srak; usually to Parker's disgust.
- Professor Mmaa's Lecture: Professor Soul's Second Assistant, a termite who is a born snitch—literally. He's been born with auditory organs all over his body and is constantly registering so much input that he feels a physical need to dump this baggage out of his memory onto a number of interested termites.
- Tortall Universe: In Trickster's Queen, Sarai Balitang refuses to not speak out against the horrible injustices perpetrated by the Copper Isles' ruling family. The things she says are accurate, but the Rittevons are notoriously paranoid and touchy and have already arrested one very popular nobleman for trying to tactfully suggest that they not be quite so brutal, so it's a really bad idea. She also tells members of her social circle where there are anti-listening spells, another unwise move.
- In Gathering Blue, Kira tells councilman Jamison that her dyeing teacher claimed that the woods surrounding the village aren't actually full of "beasts." This gets Annabella killed, since the council invented the beasts in order to scare the villagers.
- An episode of ER has two nurses talking about the two children of a patient who had been in an accident comforting each other... which ended up leading to BrotherSister Incest. Unfortunately, they unknowingly were walking past the patient's husband, leading to a near-shooting incident (the father managed to calm himself down and came clean about what he had nearly done). The doctors were not pleased about the violation of Patient-Doctor Confidentiality and the incident it nearly caused.
- JAG: In "People v. Rabb", when Admiral Chegwidden says that what he's about to say is sensitive, Bud replies that My loose lips will sink no ships.
- Boyd Crowder's latest heroin shipment was delayed and to placate his dealers he tells them that the shipment is arriving tomorrow evening. The next day one of the dealers is approached by a female junkie who offers to give him a blow job if he tells her when he will get new heroin. He obliges and sure enough Boyd's shipment is hijacked and the men guarding it are killed.
- One would think that a mob boss like Sammy Tonin knew how to keep his mouth shut about the murder he committed. However, Sammy has gone through a Villainous Breakdown and is high on drugs most of the time. He brag to his business partners about the murder and how he had help from a federal agent. One of those business partners gets arrested and trades that information to the cops.
- Once Upon a Time: Do not trust Snow White to keep a secret.
- Barbra Jean from Reba has this reputation, and for good reason. Throughout the series, she's blabbed out things quite a few times, such as telling Reba's eldest daughter and son-in-law about her youngest daughter's decision to move in with Reba's ex-husband — even after promising not to blab.
- On Turn this is a rich source of information for spies on both sides.
- When Abraham strikes up a conversation with some Hessian soldiers, he easily finds out that they are going be to quartered for the winter in the town of Trenton. George Washington uses that information to attack the unprepared Hessians and defeat them at the Battle of Trenton
- A wandering minister turns out to be a British spy. He exploits the fact that the American soldiers will talk freely with a man of the cloth and he passes any information he gleams to the British. In turn, he is discovered because a British officer talks about this in a public tavern where an Amarican spy overhears it.
- Robert Townsend became part owner of a tavern specifically so he would be able to eavesdrop on British officers talking too openly after they had a few drinks. His business partner is a Loyalist but uses the trope himself to get scoops for the newspaper he publishes. Robert is thus able to sneak into his partner's office and read a story that is supposed to be published in a few days after a surprise British attack has been launched. Robert passes the information to the Americans who attack first and rout the British.
- "Secret" by The Pierces (which became the opening theme for Pretty Little Liars) paraphrases the quote at the top of the page: "Two can keep a secret if one of them is dead".
- "Loose lips sink ships" is in the chorus of "Slip Of The Lip" by Ratt.
- A line from Taylor Swift's "I Know Places":
Loose lips sink ships all the damn time
Not this time.
- Fallout: New Vegas includes propaganda that's related to the common loose lips sink ships posters. At Helios One, it includes the "telling your wife" scenario, and "telling your drinking buddies", showing the route on how information reaches the Chinese spies.
- Mass Effect 3: The Alliance News Network twitter updates on the Reaper invasion of Earth, which included details on where civilians were able to get military protection so they could escape Earth. Emily Wong realized too late that the Reapers had been reading the tweets to find out where the evacuation point was so they could attack it.
- BlazBlue has this trope used to rather devastating effect against its invoker. After a fight, Hazama tells Makoto, in no uncertain terms, about Relius Clover's "random and untoward" interest in her before making an attempt on her life (and getting frozen by Jin for it). He really should have picked a better compliment in hindsight. Why?
- The Private Snafu short "Spies": Snafu brags about how he'll never tell the secret information he knows, but he carelessly drops hints which are eagerly picked up by hidden spies.
- Norman McLaren of the National Film Board of Canada was even less subtle in Keep Your Mouth Shut with a cackling Nazi skull thanking all the blabbermouths in Canada for giving away such good intelligence.
- As mentioned above, the Trope Namer is the slogan from World War II, reminding people to be careful what they talk about in public, lest Axis spies pick up valuable clues.
- Another poster showed a Nazi putting a puzzle together that said "The Convoy Sails for England Tonight". The caption was "bits of careless talk are pieced together by the enemy."
- Journalist Geraldo Rivera in early 2003, while Rivera was traveling with the 101st Airborne Division in Iraq during a Fox News broadcast, Rivera began to disclose an upcoming operation, even going so far as to draw a map in the sand for his audience. The military immediately issued a firm denunciation of his actions, saying it put the operation at risk, and nearly expelled Rivera from Iraq.
- Parodied by The Daily Show, which saw this as Rivera getting overexcited about establishing his Intrepid Reporter credentials.
Stephen Colbert: He's the only reporter out here who's got the cojones to walk it like he talks it! He can't be constrained by concern for the safety and security of men who have invited him to join them at great risk to both themselves and their military objective! If he gets everybody killed, so be it. He's not gonna pussy out.
- As a general rule, war correspondents are supposed to avert this by saying things like "This is John Smith, reporting from somewhere in X" rather than "This is John Smith, reporting from City Z in the nation of X" unless the story being reported is the fact that they just took Z, to keep anyone on the other side who is listening in to the broadcast to figure out where there enemies are.
- Parodied by The Daily Show, which saw this as Rivera getting overexcited about establishing his Intrepid Reporter credentials.
- News of the impending attack on Goose Green during the Falklands War was released by the British government and broadcast on the BBC World Service while the troops were still advancing on the town (and hadn't yet been detected by the Argentinian forces).
- Japanese sub-hunters during World War II habitually set their depth charges to a depth shallower than the diving capacity of most US submarines — until a Congressman mentioned this in a press conference. The Japanese immediately started setting their depth charges deeper, likely costing several submarines and their crews because one of their elected representatives couldn't keep his mouth shut.
- Nondisclosure agreements (NDAs) is what supposed to keep people from talking in regards to business deals or other sensitive information. If the person breaks the NDA, they can be fined, lose their job, or get sued, depending on the circumstances.
- People that work as Public Relations (or PR) are tasked with making sure that whatever is said about their company doesn't break any rules or paint the company in a bad light, even if it's the truth. Interviews are usually done through a PR or with someone who has a PR on standby to make sure that person doesn't say anything damaging. This is also a legitimate reason why social media accounts belonging to employees are monitored. People have been sacked for speaking out on social media in a way that brings bad publicity to the company.
- in 2015, a localizer for Nintendo of America appeared on a podcast to talk about Nintendo related topics. One of the topics the person talked about was why Nintendo doesn't bother localizing certain games. Not only did the localizer break the nondisclosure agreement, but his loose lips also made Nintendo look bad by basically telling people that Nintendo won't localize a game that they think won't make them any profits in the long run (while it is the harsh truth, it makes Nintendo look like they'll only make games that will make them money rather than making something that the fans want). The man was promptly fired.
- Tom Holland has gotten a reputation for spilling secrets for movies he's in. It's gotten so bad that he wasn't allowed to read the whole script for Avengers: Infinity War. The directors, the Russo brothers, joke about allowing him to improvise his death scene was the only way to keep him from spoiling it. He spoiled that he was staring in the film adaptation of Uncharted by posting a picture of himself playing the games "for research" to Instagram. His casting has yet to be officially confirmed by Sony. He even spoiled the plot of Jurassic World: Fallen Kingdom to Chris Pratt despite Pratt being the star of the movie.