Loose Lips

"Three can keep a secret, if two of them are dead."

- Benjamin Franklin

When someone gives away sensitive information unintentionally because they can't keep it to themselves. The Trope Namer is the famous slogan from World War II "Loose Lips Sink Ships".

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.

Due to the fact that Technology Marches On, it's even easier than ever to get people killed by running your mouth off, thanks to websites such as Live Journal, Face Book, TV Tropes, 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." )

When this is subverted, it can become Feed the Mole.

Films -- Animation

 * 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 find it.

Films -- Live-Action

 * 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.

Literature

 * 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."

Live-Action TV

 * 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 Brother Sister 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.
 * 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.

New Media

 * The Other Wiki has an entry explaining the dangers of putting sensitive information (or at least, information that can come back to bite you in the ass) on Wikipedia.

Video Games

 * 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.  realized too late that the Reapers had been reading the tweets to find out where the evacuation point was so they could attack it.

Web Original

 * Doctor Horribles Sing Along Blog: The eponymous Ineffectual Sympathetic Villain has a blog, which he uses to talk to his fans about various things he's done and his plans for future schemes.

Western Animation

 * 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.

Real Life
"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 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.
 * "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.


 * 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).