Cannot Keep a Secret

A classic sitcom trope, in which a character seems to be physically incapable of keeping a secret for very long, at least without showing extreme discomfort. Usually, by the end of the episode, or even within the same scene, they would spill the beans. Although sufferers of this trope in fiction are mostly women, due to their more gossipy nature, there are male examples too.

Almost always Played for Laughs. Related to Keeping Secrets Sucks. Compare Can Not Tell a Lie.

Anime

 * Haruna Saotome in Mahou Sensei Negima: only minutes after threatening to torture her friends for not letting her in on The Masquerade earlier, she proceeds to start telling the next people she sees, somewhat justifying their decision not to tell her. She also comes very close to telling Anya about Negi's Pactios.
 * Miyuki of Smile Pretty Cure has a very poor time keeping her secret identity... and the secret identities of her teammates.

Comic Books

 * There's an example in Yann et Julie, an old and obscure Franco Belgian Comics book: In one of the skits, Yann sees Julie coming out of a shop during Christmas Holidays, having ordered an item. He presses her to tell him everything about this, but she's dubious as she knows he can't keep secrets. After he swears he will keep it, she reveals she'll offer the new Nintenga to one of her friends. Sure enough, once they part ways, Yann goes to the shop to get info about the order, and while the clerk can't tell him any name, he gives him the phone number he has to use to tell when the order will be available. Yann rushes to his house, dials the number, and right off the bat, thinking he's talking to Julie's friend, starts to spill out about the present... Only to hear the voice of a furious Julie: in his excitement, he didn't notice it was her phone number.

Film
"Sam: Can you keep a secret? Flint: No. *beat, then realization* But, but, but this time, sure, yeah."
 * From Cloudy with a Chance of Meatballs:

Literature
""Shouldn't have said that, should not have said that.""
 * Rubeus Hagrid from Harry Potter is described by several characters as being "less than discreet", despite his best efforts to the contrary.

Live Action TV
"Emma: See? You both suck."
 * Lily Aldrin on How I Met Your Mother can't keep a secret for her life.
 * Marshall also can't keep secrets specifically from Lily.
 * Ted can't so much not keep secrets as he doesn't understand why something should be a secret unless specifically told so. For example, when Stella told him, he immediately told the rest of the gang, much to her annoyance.
 * In a first season episode of Charmed, Phoebe learns that their handy man, Leo is essentially an Angel. She tells her sisters by the end of the episode but they don't believe that Leo is magical, which is odd considering that they are themselves witches...
 * To a lesser extent, Paige Cannot Keep a Secret. In Season 4 Piper told her not to tell Phoebe that they suspect Cole of being a demon. Paige almost immediately does afterwards.
 * Virginia on Raising Hope encourages others to blackmail her with a secret of her own to avoid blabbing theirs. This backfires when her family notices her "gossip face" and she ends up telling them her own secret.
 * Cheers: In "Truce or Consequences", Carla confides in Diane, only for Diane to turn around and blab the secret to Coach less than 24 hours later. (Well shy of the purported 47.)
 * Of course, it turns out
 * An entire episode of Corner Gas revolved around Brent and Lacey competing to see which one of them is a better confidant.

"Gypsy: Can you guys keep a secret? Crow: Never have, never will! Haha!"
 * This happened with Monica in Friends. Monica learns that Gary is gonna ask Phoebe to move in with him, and asks that she doesn't tell Phoebe. Monica manages to hold out for a full 25 seconds before blabbing.
 * Saturday Night Live: Kristin Wiig's character Sue, who is almost orgasmic in her desire to tell a secret, usually involving parties. (Sorry for the ad at the start of the video.)
 * Averted in Scrubs; Carla usually can't keep secrets, but when Eliot loses her job at another hospital, she manages not to tell Turk and J.D. about it. Of course, they can tell she knows something ... so she tells them she's keeping the secret that Eliot smokes a pipe.
 * It's happened to Fran Fine a number of times on The Nanny, like in "One False Mole and You're Dead".
 * Elaine from Seinfeld will spill the beans if you give her schnapps.
 * Grizz and Dot Com (apparently) on Thirty Rock. Liz and Tracy tried to invoke this to create a rumor, but it backfired and they got burned by Gossip Evolution.
 * Mystery Science Theater 3000: Mitchell:


 * The Big Bang Theory: Sheldon can't do impromptu secrets. So he goes way, way overboard constructing elaborate, and usually unnecessary, lies. They fall apart because Sheldon.
 * Michael Scott from The Office frequently blurts out people's secrets. On several occasions it's been due to him showing off what he perceives as a close friendship (evidenced, in his mind, by the fact that they confided in him in the first place) with the person whose secret it is.

Manga

 * In Hajime no Ippo, pretty much every member of the Kamogawa gym is like this. Every time Ippo tells a fellow member to shut it about something he will do (like a date with Kumi), the whole gym knows the day after. Itagaki is the most notable offender of this though: not only does he tell Mashiba the details of the relationship between Ippo and Kumi, but when the same Mashiba tells him a secret of his own, while Itagaki swears to keep it we see a pannel showing how impatient he is of telling everyone at the gym!

Newspaper Comics

 * Edda in 9 Chickweed Lane is an unrepentant gossip, who gets offended if she finds someone (like Amos) who can keep a secret.

Web Comics

 * Rudy in Rain is known to be bad at keeping the secret that Maria is a lesbian, among other slips.

Web Original

 * Krillin in Dragon Ball Abridged becomes this whenever he gets nervous, which happens to be a lot. One time he nearly blurted out where he and Gohan came from to Freeza before Gohan stopped him (though Dende revealed it right afterwords).
 * The Nostalgia Critic is usually good at keeping his promises, but when it comes to secrets he can't seem to help himself.

Western Animation
"Marge: I've got to tell Homer about this baby in just the right way and at just the right time. Until then, please, keep this to yourselves. Patty: Oh, if he found out now, it would probably destroy him, huh? Marge: Oh, yes. Patty and Selma: *exchange evil grins and get up* Gotta go! Marge: Wait a minute! Wait, I know that look. Now promise you won't tell Homer. Selma: Oh, we promise we won't tell...Homer. Patty: Hello, is this A. Aaronson? It might interest to you to know that Marge Simpson is pregnant again. later Patty: on the phone with a weary voice Just thought you'd like to know, Mr. Zykowski. hangs up, sighs There. Aaronson and Zykowski are the two biggest gossips in town. In an hour, everyone will know."
 * Arthur: DW is desparate to be told a secret, any secret, which she then tells other people - because what's the point of knowing a secret if you don't tell? She eventually learns An Aesop about keeping secrets.
 * It's also a Running Gag that Arthur's best friend Buster just cannot keep a secret - whenever Arthur tells him a secret, he'll promise to keep it and then promptly loudly inform the person closest to them that he's got a secret to tell them. When Arthur is still standing right there.
 * The Simpsons: in a Flash Back episode to when Maggie was born, Marge begs her sisters Patty & Selma to not tell until she's ready to inform her husband.
 * they go to the phone book and open it to page one*

"Bart: No Dad, I will not tell another another living soul...*listens on phone*...No, not even Milhouse. Bart: Hey Milhouse, can you keep a secret? Milhouse: No. Bart: Oh, who cares! Michael Jackson is coming to my house!"
 * Also used in "Stark Raving Dad" when Homer's friend (supposedly Michael Jackson tells Homer to ask Bart to keep his visit a secret.
 * Bart hangs up phone, before struggling to keep his hand away. He submits and quickly dials Milhouse*


 * Also played with in another episode, where Homer overhears Moe proclaim he'll give a free beer to the gossiper "Mr X" (Homer's secret alias). Homer whispers if Moe can keep a secret, he claims no, not even a little one.
 * In the "Green Isn't Your Color" episode of My Little Pony Friendship Is Magic, one of the recurring jokes is Twilight's extreme difficulty in not telling secrets (particularly because of the irony in that telling said secrets would almost immediately solve the episode's conflict).
 * Jimmy Two-Shoes can't keep secrets when he's excited. Even when Beezy can.
 * In the pilot episode of The Dreamstone, the Dream Maker insists Rufus promise not to tell a soul about the Dreamstone's existance. Within five minutes, he brings Amberley up to the tower to look.
 * Don't tell Alex to keep a secret. Just don't.
 * One of the characters in Little Dogsonthe Prarie is this. The second he's told a secret, he blurts it out for all to hear.