The tattletale. The blabbermouth. The squealer. That no-good snitch! You can't go through life without having the misfortune of coming across someone who's willing to rat you out and get you in trouble.
However, the motivations of the snitch and how they're regarded in a story can vary wildly. Snitches have the reputation of being cowardly weasels, but there are times where a snitch can be responsible or heroic. Due to the sheer prevalence of this trope, there are several important variations:
Petty Patty/Peter: A character that's jealous of the main character or has a petty reason to dislike them, and thus relishes the chance to get them in trouble. You can usually spot them smiling smugly as the main character is chastised for whatever they did. Naturally, they're going to get some payback.
Concerned Claire/Corey: A character that turns in a friend or associate out of genuine concern for their well-being. Maybe their friend is sliding towards becoming a Well-Intentioned Extremist, maybe they're compromising their cause, or maybe they're going to land themselves in jail ...or worse. This character is willing to nobly take any hostility from their friend, because they'd rather see them alive and safe than continue what they were doing. Whether their concern is responsible or misguided can vary.
Whistleblower Wilma/Wilson: A character who sees a villain - or even a hero - breaking the rules and turns them in because of their own moral conscience. The most heroic of all snitches, many whistleblowers risk their friendships, careers, or even their lives to tell the truth.
Disgruntled Daria/Davey: A character that dutifully gives information to their superiors but is then unsatisfied with how they deal with it. If they won't listen to her, then she'll find someone who will! This kind of snitch can vary wildly; sometimes the authorities refuse to listen, so they secretly tell someone else who will take action. However, sometimes the authorities are just acting in a way she doesn't like and thus is going to force their hand. This latter variation can be considered treason and can cause internal strife.
Betrayer Barry/Belinda: A character that sells out their own friends to save his own skin. Maybe they've gotten caught and offered a plea deal, maybe the authorities are offering incentives, or maybe they're just jerks. Either way, this character can end up in a lot of trouble if his friends find what he did ...
Snobby Sara/Simon: A character that turns in any other character, no matter what reasons they had for what they did. They broke the rules, so those little punks have to suffer the consequences! This character doesn't care about justice or rules as much as they enjoy feeling smug and superior to others.
Obnoxious Olivia/Oscar: A kid character that tattles on someone else for ... well, the thousands of reasons why kids like getting people in trouble. Usually played for laughs, but can sometimes can be taken more seriously, especially if the kid is a young whistleblower or is called a liar.
Innocent Ingrid/Isaac: A character who, along with other characters, has been involved in some activities that have gone rapidly downhill, and turns them in because of this. Maybe they never wanted to do anything bad but suddenly found themself caught up with people prepared and willing to do so, maybe their co-conspirators began doing things that they cannot stand, or maybe they honestly didn't know that their friends or co-workers were doing anything wrong and upon finding out, decide to turn them in.
Drug Doug/Debbie: A character who ends up blabbing about activities to another person without realizing it because they were under the influence of drugs or alcohol. Also a Truth in Television, as drugged people or drunk people often blab the truth at the most inappropriate times due to their inhibitions being loosened. Can sometimes fall under Lacerated Larry if the person was drugged as part of an interrogation.
and, more sympathetically
Lacerated Lacey/Larry: A character that was simply torture interrogated to the point of having the information beaten out of them. In many cases, the person may have been an extremely loyal comrade and in normal circumstances would not have ratted out their team. But since Torture Always Works and the cold hearted villains have ways of making victims talk, the captured member will always be left screaming in the end.
Snitches vary from Gossipy Hens because they're actually telling the truth and usually telling it to a recognised authority, whether it's a parent or the government. This can lead to a lot of Moral Dissonance, because no matter how much of a jerk a snitch might be, the characters wouldn't have gotten in trouble if they hadn't done something snitch-worthy in the first place.
See also The Informant, of which this trope is a Sub-Trope.
In Naruto, Shizune goes to Homura and Koharu regarding Tsunade allowing Naruto to go on missions where he might encounter the Akatsuki. She's clearly a Concerned Claire over Naruto's well-being, where Tsunade is far more inclined to take it on faith that Naruto will make it out alright. She gradually begins to accept Tsunade's reasoning, but when she does, the elders come in to attempt to restrict Naruto's movements based on what Shizune told them, and in the anime, Tsunade gets quite upset with Shizune.
In Guilty Crown, Yahiro ends up selling out the protagonist to secure treatment for his sick little brother. Especially jarring since he used to be an admired friend of Shu's, who was under the impression that they had sucessfully talked over their differences. Even after Yahiro returns to being a permanent member of Shu's group, the tension created by this event remains between them for most of the series, leading to several "Silence, Traitor!" moments.
In the One Piece anime, one of the slaves on Tequila Wolf reports Robin to the others when being threatened with punishment, and is rewarded with a box of chocolates. She, however, is overcome with guilt, and gives it to Soran, who goes to give it to Robin.
In Turn 19 of Code Geass, after Schneizel meets some resistance to the Black Knights in his efforts to goad the Black Knights into turning on Lelouch, Ohgi and Villetta's account of Lelouch's geass end up sealing the deal. Quite possibly a Petty Peter for Villetta, and a misguided Whistleblower Wilson for Ohgi, considering some ofthe evidence.
In the manga version of Neon Genesis Evangelion, Kaji was a Betrayer Barry when he was a kid. He and his friends were stealing food and supplies from a military base. Kaji was caught, and gave up his friends to the soldiers to keep from being killed. The soldiers killed his friends, and he's been haunted by Survivor Guilt ever since.
In Bokurano, Tamaki "Komo" Komoda is an Innocent Ingrid, since she is the one who tells the authorities about the kids piloting Zearth once it becomes clear what they've gotten involved in. In the manga, she goes to her father, who is an admiral, after a few battles have taken place. In the anime, while the group is being questioned by the police after the second battle, she tells them that they were piloting the robot.
In Identity Crisis, Wally West averts this trope, even though he'd fall squarely into the Whistleblower Wilson category, when he decides not to tell Superman and Batman that a group of Justice League members have been wiping supervillains' memories via Zatanna to protect their secret identities, even when he learns they went so far as to effectively lobotomize Dr. Light and, when Batman found out and objected, mind-wiped him as well.
Becky of the Sin City story The Big Fat Kill falls squarely into Betrayer Belinda territory. Her reason for selling out Gail and the other girls of Old Town was that Manute and the mob offered her a way out of being a prostitute, something the girls of Old Town never did. It didn't help that she wasn't willing to let the girls of Old Town protect her mother, who she kept her life as a prostitute a secret from.
In Bullitt, Johnny Ross, a Chicago mobster who agrees to testify against the Mafia. Naturally, the Mafia wants him dead for this—and for the money Johnny stole from them.
Inside Man: The reason for the owner of the bank not wanting his diamonds to be discovered, and the reason why the protagonist gets away with it..
In Toy Story 3, Chatter Phone was the Lacerated Larry type: he ended up confessing to Lotso and his minions about Woody and the others escaping from Sunnyside from what was implied to be torture.
The film version of Order of the Phoenix made Cho Chang into a Lacerated Larry. Dumbledore's Army was initially angered at her betrayal, but then it is revealed that the only reason she squealed was because Umbridge fed her a drink laced with Veritaserum, thus literally leaving Cho with no choice but to spit out the existence of Dumbledore's Army.
The admiral in the 2009 Star Trek movie also ended up a squealer to the Romulans, specifically as a Lacerated Larry, because after he left the ship, they interrogated him and implanted a bug into his system that forces him to reveal everything he knows about Starfleet Academy.
In The Berenstain Bears and the Scandal Sheet, the members of the student underground newspaper, including Brother, get exposed and in trouble for making a false statement about a teacher dating someone when Brother tells his sibling about it, who passes the word to Mama who then informs the authorities. This is a case of a Concerned Claire that actually turned out for the better, as with the exposure, the real student newspaper was able to be reformed, making the student underground unnecessary.
Stelli, in Paula Volsky's novel Illusion, is somewhere between a Petty Patty and a Disgruntled Daria: She blames Spoiled Sweet heroine Eliste—for whom she used to work as a maid—for being unable to save her fiancé's life (and in all fairness, Eliste tried) and sells the noblewoman out to the revolution. Eliste gets away.
Tuller, in the Col Sec Trilogy, sells out the main characters to the cops—supposedly to make them leave his gang alone, but it's made fairly clear that he mainly just did it to be a jerk. The rest of the gang are dubious about this to begin with...and when they find out that the cops have no intention of keeping their end of the bargain, they turn on Tuller and knife him.
The book version of Harry Potter and the Order of the Phoenix has Marietta Edgecombe snitch on Dumbledore's Army instead of Cho Chang. She's portrayed as a Betrayer Barry and is left with the word "Snitch" written across her face in boils because Hermione hexed the club's roster sheet.
Nelthilta, the silly young Efrafan doe from Watership Down, is a variant of the Lacerated Lacey; she's overconfident and gives one too many obvious hints about the upcoming escape plan to the Efrafan officers. Realizing that something is amiss the officers imprison her and torture her into spilling the beans completely.
In A Stainless Steel Rat is Born, Jim, remembering how he decided to pursue a criminal career, recalls a childhood episode in which he framed an Obnoxious Oscar schoolmate for shoplifting. This lad was known to the student body as Smelly, and tattled on other children for the simple pleasure of it.
Jayne of the Firefly episode "Ariel" tried to turn in the Tams to the Alliance during the hospital heist due to him generally resenting the Tams and wanting them both off the ship for a variety of reasons, and due to River recently slashing him with a butcher knife and his concern about her doing it to anyone else. The reward money that the Alliance were offering wasn't a bad incentive either. Jayne was somewhere between Petty Peter and Betrayer Barry, but after Jayne got betrayed himself and arrested right along with them, he decided to get both Simon and River out. He still had to face the airlock and a very pissed off Mal because of what he did though.
The culprit in the episode "Mr. Monk and Mrs. Monk's" main motivation in trying to intercept various documents and tapes that detailed journalistic work that Trudy Monk and Janice worked on was because one of the tapes contained evidence that he was the person inside the dock union who was involved in ousting the former president from power due to corruption charges, and it is heavily implied that had his fellow union workers discovered his involvement, he'd be in deep trouble with his "friends."
Mr. Monk and the Dentist had a Drug Doug type from the murder "victim" of the week: The victim (an ex-cop who went renegade and started robbing armored trucks) ended up having to go to the dentist for a chipped tooth that he got in a scuffle with one of the armored truck drivers during a heist (he was technically a cop, so he was on their dental plan). While going through the routine anesthesia, the ex-cop, evidently under the anesthesia's influence, blabbed to the dentists working on him about the heist as well as the hiding place for the money, to which the dentists stole the money. Unfortunately, he, either from lingering memories of what happened, or having put two-and-two together, found out about their robbing his ill-gotten bearer bonds and confronted them, leading to his death at the hands of the dentists. The dentists later attempted to have Monk tortured at the Dentist's office, although they weren't able to get much out of him before they ended up arrested by Disher and Stottlemeyer (the former of whom spent most of the episode as a Cassandra Truth witness to the aforementioned murder while he himself was under anesthesia).
In "The Telling", a third season episode of The Middle, we learn that Frankie has been rewarding Brick for years with candy cigarettes for informing on his older siblings.
Scandal: Justice Verna Thornton becomes a Betrayer Belinda in "Blown Away". Vice President Sally Langston wants Verna out of her Supreme Court seat, while Verna has only a few months to live before she dies of cancer. So Verna offers her a choice: either take her resignation or take the paper revealing the identity of the President's shooter. Sally takes the identity revealing paper and Huck is arrested. Verna had put two and two together to figure out that Huck supposedly shot the President. Huck didn't do it, and Verna doesn't know that. So it's ambiguous if she was doing this to selfishly keep a job she only gets to have for a few months or if she did it because it's her duty to take down whoever shoots the President.
Lifesaver from Mega Man X reported to Signas that Zero was actually getting stronger when infected with The Virus. When Signas wisely decides not to act rashly, Lifesaver snitches to Zero's best friend X instead. The resulting misunderstanding and tension results in a battle between the two that nearly gets both friends killed.
Sidonis from Mass Effect 2 is a Betrayer Barry. Part of Archangel's squad on Omega, he was caught by the mercenary gangs and ended up betraying Archangel to save his own skin. Depending on how you deal with Garrus's mission, he'll either end up dead by Garrus's hand or he'll be given a chance to redeem himself after admitting his guilt.
In an early Blood Elf starting quest in World of Warcraft, the player is asked to find a book for two apprentices. When the book is drenched in water, the apprentices tell the player to take the fall for them, since the player won't be punished much. Instead, upon reaching their master, you tell him what they told you to do, and he has you hit them with a rod that turns them into animals.
In the old Skool Daze video game on the ZX Spectrum, a randomly triggered event reveals that Einstein is going to report the player. The player must prevent him from getting to the teacher or else get assigned lines; receiving 10,000 of them results in a Game Over.
Metal Gear Solid 3: Snake Eater: Even though Raikov is supposed to be Volgin's gay lover, interrogating him at knifepoint will have him dish out information about some weaknesses of Volgin for Snake to exploit, such as the fact that Volgin is weak against water or that Russian Glowcaps will deflect his electric attacks.
In Peace Walker, anyone of the FSLN who is captured by the Peace Sentinels ends up being tortured until they squealed their comrades' location from it. They end up killed later on. Chico is the only one who managed to live after breaking from it (and even then only because Big Boss rescued him before they could get the chance to execute him).
According to Dr. 0, Dr. Borous spent high school "commie-fink tattletal[ing]" on the kids he disliked in the backstory of Fallout: New Vegas: Old World Blues.
In Lucky Dog 1 Homer tries to persuade Gian, the player character, to become one of these as he falsely believes Gian (a member of the mafia) hates criminals due his parents being murdered and the criminal never getting caught. There's no option to become one as Gian is completely loyal to the mafia but there is an option to attack Homer, who told the guards to stay away from the room believing Gian would agree to be a rat.
In the Chick Tract "The Last Generation", Bobby turns in his grandfather for being a Christian in order to get a reward. One of the Christians, Paul reveals the location of the cabin where Connie and Charles are hiding, afraid of being caught and tortured.
Sarah from Ed, Edd n Eddy is the Obnoxious Olivia. She is a Spoiled Brat who is favored by her mother more than Ed. She always threatens Ed to do her bidding or she'll "tell mom." It doesn't help that their mother just goes along with Sarah. Other times, she tattletales on him for petty things!!
Candace from Phineas and Ferb seems to vary between Snobby Sara, Obnoxious Oliva, Concerned Claire or Petty Patty, depending entirely on the writer.
Aaahh!!! Real Monsters: Zimbo, he not only acts as the Snorch's Familiar, he also acts as the Gromble's personal spy who reports back any unruly behavior by the other monsters, plus he's the only one who understands the Snorch's speech clearly.
Randall,Randall,RANDALL from Recess is The Obnoxious Oscar and HOW!!??
He has reservations, however. For one thing, he never tries to directly squeal on those who are higher up than him (such as King Bob), and gets legitimately angered at those who do end up doing something like that. In addition, in the ending of the movie School's Out, Randall was noticeably disgusted with Fenwick desperately trying to avoid jail time by pinning his boss, Dr. Phillium Benedict, with the entire blame on the events of the movie, and even offering evidence for the state trial.
In the episode where Principal Prickly is accidentally hypnotised to act like a six-year old, when TJ and his friends decide to keep it under wraps, Randall overhears them. Unlike most other times where he usually takes joy in snitching, his snitching about what happened to Prickly falls more under the Concerned Claire subtype, as he expresses genuine shock and horror and rushes to Finster to tell her of what happened.
"A Day at the Zoo": As a spot gag described in the picture above.
"Don't Axe Me": The Barnyard Dawg squeals on Daffy for Elmer to catch him.
"Buccaneer Bunny": One parrot keeps telling Pirate Sam where Bugs is hiding until Bugs himself puts him out of his misery with a stick of dynamite.
Parrot: Me and my big mouth.
"Tom Turk and Daffy": Daffy squeals on the Turk because of his temptation to Yams.
The short "Big House Bunny" ends with prison guard Sam getting arrested for freeing convict Bugs when he's pushed to his limit. When he asks who was the stool pigeon who squealed on him, it cuts to Bugs, who looks at the camera and starts cooing like a pigeon.
"Bart the Daredevil": Despite trying to convince Bart the dangers of daredevil stunts, Lance Murdock is instead impressed by Bart's interest in it, which causes Lisa to tell Homer about it, fearing that he may get hurt or die despite getting the most attention.
"Mypods and Broomsticks": Lisa squeals on Bart after pulling a prank on Steve Mobbs and the rest of the consumers and employees.
Martin Prince is also one when he squealed on Bart in "Bart the Genius" and on Milhouse in "Summer of 4 Ft. 2".
The whole episode of "The Seven Beer Snitch" focuses on this trope.
Robin in Batman Beyond: Return of the Joker qualifies as a Lacerated Larry. After the Joker kidnapped him, he subjected him to three weeks of shock and serum-based torture before he ends up breaking from it and confessing everything he knows about Batman, including his secret identity.
In Batman: The Animated Series, Earl Cooper was a Whistleblower William who was nearly killed by his bosses for trying to go public about a potential lethal safety defect in his company's newest model of car and was saved by Batman. He lost his job and was living on the streets when Batman saved him again... by tracking him down and hiring him to design the Batmobile.
A World War II-era cartoon had a guy bragging about his being entrusted with keeping a secret. Unfortunately, he ended up becoming exceptionally drunk, and told the nearest woman in the tavern about his secret (being on a ship and its coordinates), who also turned out to be a Nazi spy, resulting in his death and the implication that he went to hell for it. In other words, he acted as a Drug Doug on himself. This cartoon can also be seen at the International Spy Museum.
Mako in The Legend of Korra is a Concerned Corey in the episode "Peacekeepers", ratting Korra out to the President to prevent her from doing something completely irrational and escalating the Water Tribe's civil war.
Cameras near traffic lights and roads. They tend to take photos of you going even 3 miles above the speed limit or take photos of you running the red light. The photos go to the department and you end up getting a ticket mailed to you.
There are special statutes called "Whistleblower Laws" for Disgruntled Darias who report wrongdoing within an organization to its own internal authorities, see it not acted upon, and then take it to civil authorities (i.e. police). They are meant to protect such "whistleblowers" from retaliation. How well this actually works in practice varies widely.