In Fruits Basket, Rin gets physical with Tohru and ever since their first meeting e.g. grabbing her by the collar, roughly rubbing her head, etc. The moment Kagura nails Tohru (and accidentally knocks her out) in frustration that she won't confess her feelings to Kyo so that Kagura wouldn't have to think about him anymore, Rin gets the angriest anyone has seen her in the story.
In Ore Imo, Kyousuke constantly jabs Manami about how normal and plain she is, but when Kirino offhandedly makes a similar remark about her, Kyousuke has this to say:
"I hate hearing someone other than me badmouthing her!"
A Foreshadowing of sorts, this trope also (somewhat) applies to the Little Sister Heroine Kirino herself. When her friends Ayase and Kanako come over for a visit they hear her constantly berating Kyousuke (which the poor man overhears), but once Kanako adds her own words, Kirino stays silent instead of agreeing with her.
Shannon Casull teases his little sister Pacifica mercilessly in Scrapped Princess, but he literally swears to oppose god itself in her defence, even if it means the destruction of the world.
In Psyren, Fredrica often bullies Marie. However, when someone else threatens her, targets her, and/or makes her cry, she goes ballistic.
Inui, who cruelly beats his brother, Saburou, nearly constantly, claims the world is too cruel for his brother, spouting, "I'm the only one allowed to hurt him!" But it comes out creepy as opposed to heartwarming...
Skip Beat! invokes this trope in chapter 88 of the manga. Sho and Kyouko were once friends, but no one could call their current relationship "friendly." Yet when Sho's position as a top musician is threatened by a new band, Kyouko lashes out at the face of the band, and yells "I am the only one allowed to defeat him!" He can fall to the darkest depths, sure, but she has to be the one to put him there.
A rather dark version of this happens in X/1999. Despite murdering Subaru's beloved sister Hokuto as well as constantly trying to kill Subaru himself, Seishiro gives Subaru one of his eyes upon his death to replace the one he lost to Fuuma/Dark Kamui. The reason given is that he didn't want a mark left on Subaru that he himself didn't make.
Ranma ½: Ranma and Akane are one of Rumiko Takahashi's most famous fictional couples, known for their Belligerent Sexual Tension, so it's no surprise that they've insulted each other more times than you can count. But when Kodachi's rival, Asuka, calls Ranma a fool, Akane gets pissed and actually has Ranma go out on a double date with Kodachi and Asuka to prove how handsome and cool he really is, despite being the jealous type. She even helps dress him up and follows them on the date to make sure everything goes smoothly! Which, of course, it doesn't.
Yui: Because the only one allowed to make fun of you is me!
Tomoe from Kamisama Kiss normally is sarcastic, rude and highly critical of just about anything Nanami does. But should anyone else insult her and/or criticize her he is quick to come to her defense.
In the beginning of Pandora Hearts, Alice calls Oz her property and protects him from people who want to hurt him, but will consistently hit him herself.
Alice: Nobody touches my PROPERTY! And Oz is my manservant - therefore, he is my property!
Vegeta plays with this occasionally during in Dragon Ball Z with regards to Goku. He occasionally becomes very, very slightly concerned for Goku's safety when Goku goes off to fight someone else, even offering occasional bits of help and support - mostly because he believes if anyone's going to beat Goku in a fight, it should be him. This is most notable just before Vegeta's death in the Freiza saga, and the early stages of the Main Buu saga.
In Secret Wars, one of Marvel's first Crisis Crossovers, tensions rise between the X-Men and the other Marvel heroes out of distrust (though most of them have worked with the X-Men in the past at least once, so they really should have known better). When Hawkeye gets in Cyclops' face, Wolverine cuts in and says, "Cyclops might be a jerk, but he's our jerk!"
A recurring trope for the Thing of the Fantastic Four — he will constantly threaten, shove around, fight with, and even beat up the Human Torch, but the moment anyone else lays a finger on him, Ben will exclaim "no one hits Matchstick but me!" and will not stop until the villain has been pummeled thoroughly. Johnny Storm reciprocates similarly — he is constantly making fun of and playing cruel pranks on the Thing while showing little to no sensitivity about his monstrous appearance, but will furiously leap to his defense if anyone else hurts Ben's feelings.
In The Sandman, Cain goes absolutely berserk when The Kindly Ones kill Abel. Abel dies a lot of times in the series, always killed by Cain, of course. Abel also takes the event very badly judging by his last words, since it's not like he likes Cain killing him on a near-constant basis, but that's the way their story has always gone. When The Kindly Ones do it he gets upset, exclaiming that they don't even know him.
L: No one takes the piss out of Light apart from me.
Many (if not most) Fairly Oddparents fics that feature Timmy/Vicky have Vicky defending Timmy because only she's allowed to make him miserable.
In Money Train Wesley Snipes' character will be the first to call his adopted brother a fuck up... but god help anyone else who does it in front of him. Hell he won't even allow his adopted brother to say it about himself. He even angrily says to his adopted brother that he "keeps fucking up" rather than he "is a fuck up" when his adopted brother admits he is one.
In The Goonies, there is a deleted scene where the bully Troy is going to punch Mikey when Brand stops him, saying, "Nobody hits my brother except me."
In Hot Shots!, Admiral Bensen beats up Lt. Cmr. Block when it becomes clear that he has needlessly endangered the other characters. "That's my job!"
In Rise Of The Guardians, Bunnymund has no qualms mocking Jack about his lack of believers. But the moment Pitch does the same thing, Bunny immediately tries to attack him for it.
Shaolin Soccer: The monks are all creeped out by Mui's new, bizarre look and make jokes that she's a ghost. When Mui's overbearing boss arrives and insults her appearance, the monks all rush to her defense and castigate the employer, saying that she looks beautiful.
Garfield: Hey, nobody gets to mistreat my dog like that except me!
Forrest Gump: Lieutenant Dan is constantly abrasive towards Forrest, verbally abusing him at every turn in a "George and Lennie" fashion. However, he completely loses his cool when a pair of escorts he's invited over to celebrate New Year's with begin calling Forrest "stupid" and immediately tells them to get lost.
The picture book Julius the Baby of the World by Kevin Henkes is built around this trope: the jealous older sister, Lily, comes to terms with her new baby brother when she hears her cousin insult him and springs to his defense.
In the third Harry Potter book, Ron ends up getting detention from Professor Snape, after criticising Snape for calling Hermione a know-it-all when she answers a question. It is mentioned that Ron calls Hermione a know-it-all about twice a week. The rest of the class is also shown to be annoyed at Snape for that, though unlike Ron it's less about Belligerent Sexual Tension, and more about just not liking Snape.
In the Witches series of Discworld, the many branches of the Ogg family are locked in a neverending, complicated feud, but if one member ever hears a stranger badmouth a member of the family, then the Oggs will forget their differences and unite to punish the troublemaker.
Another Discworld example:
Vimes: Detritus is not my property. If I don't need a passport, neither does he.
Detritus: You know, if it's gonna be a problem, I don't mind-
Vimes: Shut up, Detritus. You are a free citizen of Anhk-Morpork. That is an order.
Archchancellor Ridcully has a similar view to his people.
Ridcully: How dare you, sir! Continue, Mr Collabone!
Collabone: I, I, I—
Ridcully: That is an order, Dr Collabone!'* *
Archchancellor Ridcully was a great believer in retaliation by promotion. You couldn’t have civilians criticizing one of his wizards. That was his job.
The book series "Cut & Run" has main characters Ty and Zane insult and annoy each other and, as a trigger for beginning a romantic (but dysfunctional) relationship, attack each other in a full-blown physical brawl, Ty even attempting to break Zane's nose. The rest of the series involves the two defending each other from various antagonists while consistently pissing each other off.
Jaime: You are speaking of a highborn lady, ser. Call her by her name. Call her Brienne.
In Myth Directions, Skeeve makes a promise without thinking, immensely complicating the book's plot. His master Aahz has plenty to say about it, but when somebody else makes the same point, Aahz snarls at them; he's the only one who's allowed to criticize his apprentice.
In Firefly, Mal calls Inara a whore all the time. But he's also the first to defend her if anyone else calls her (or implies she is) a whore. He later states that while he loathes and insults her job, he's not insulting the woman herself and actively tries to protect her professional reputation (just never to her face). On the other hand, the person who triggered his Hypocritical Heartwarming was treating Inara herself (instead of her job) like a whore, and even a slave. And mutually, their Volleying Insults could range from overprotectiveness, a defensive mechanism against rejection, or just an act to annoy each other.
In Star Trek: The Original Series, McCoy is always trying to get an emotional rise out of Spock, but in the episode "Plato's Stepchildren," McCoy jumps to Spock's defense when powerful aliens force him to cry and to laugh. And in other episodes he's usually the first to jump to Spock's defense any time anyone attacks or insults him, possibly because his issues with Spock are more of a giant angry moral debate while other people tend to be full racism.
Although it's never expressly stated, it's pretty obvious that B.A. is the only one who's allowed to be mean to Murdock and Face. He frequently verbally abuses them and threatens them with physical violence (Murdock is his main target, but Face gets quite a bit of this too, at times). And then you'll get a scene where the team is facing the slimeballs of the week; Murdock and Face, the physically weaker half of the team, frequently find themselves fighting a mook who's too big for them to handle. Cue B.A., who proceeds to knock the sucka's lights out. Five minutes later he's back to insulting Murdock and Face and threatening to beat them up himself. Happens every few episodes.
In Even Stevens Ren never hesitates to call Louis an idiot. However, after failing a band audition (big time) the guy judging it called Louis an idiot. Ren then told him that the only person allowed to call him an idiot is her.
In an episode of Family Matters, Laura dumps a boyfriend because he starts making fun of her brother the same way she does.
She also blasts anyone who dares to badmouth Urkel, despite the fact that she herself can't stand him most of the time.
There's an episode of Everybody Loves Raymond where Ray ends up in a rivalry against Peggy, the obnoxious den mother of the Girl Scouts Expy that Ray's daughter is a member of (to elaborate, Peggy has a history of bullying the other scouts' parents—to the point where they're terrified of her—in order to get choice spots to sell cookies, thus guaranteeing that she herself will win the top prizes). Ray is apparently the first parent to stand up to her, and she reacts by trying to pull his sales table away from him in public and push him onto the ground. Ray's wife Debra shows up and tells Peggy to back off. At first one is inclined to think that Debra, who usually bullies and physically abuses Ray a lot herself, is going to finally redeem herself...but then as soon as Peggy is out of sight, Debra goes back to bullying Ray, and starts sneering at him (and in later episodes such as "A Date for Peter", she uses the events of this episode to make fun of him in public). Apparently, she didn't really object to Ray being bullied...she merely objected to someone else bullying him, because she apparently views him as being her property (emphasized when she tells Peggy "if you've got a problem, you bring it up with me" as if Ray isn't his own person, and is merely just one of her possessions).
Borderline example. In Supernatural no one is allowed to call Sam 'Sammy' except for Dean.
"He's the only one who gets to call me that." Awwwww.
The easiest way to identify bad guys is that they are people who call him "Sammy." Even Lucifer was sympathetic until he called Sam "Sammy." After that, he had to die.
In That '70s Show, Hyde didn't like Jackie at all earlier into the series and would often insult her. But when a guy Jackie shows interest in to make Hyde jealous calls her a "bitch," Hyde punches the guy in the face.
In Glee, Rachel is tricked by her boyfriend Jesse into getting egged by Vocal Adrenaline - genuinely upsetting for Rachel, since 1) she's a vegan and 2) Jesse took the opportunity to break up with her. The boys from New Directions immediately mobilise to go kick Vocal Adrenaline's asses - including Kurt, who angrily insists that "Rachel is one of us! We're the only ones who get to humiliate her."
And then there's the moment when all the Glee guys, even the ones who used to bully Kurt, defend him in front of Karofsky.
Tony gets to insult McGee. You don't get to insult McGee. Tony does. Not you.
Pretty much the whole team can be like this. It is part of what makes them True Companions.
On Blake's 7, despite claiming to despise Vila, when Avon finds out that Tarrant is likely to get him killed, Avon threatens to kill him.
On The Vampire Diaries brothers Damon and Stefan Salvatore may hate each other and mess with each other all the time, but woe betide anyone else who tries to hurt or kill the other.
On Arrested Development, Michael gets this way when his new girlfriend/PR manager insults the other Bluths. Subverted in that he only defends her until she picks on his son, at which point he leaves her at the mercy of his sister and his mother.
In one Bones episode, Booth is watching Cam argue with her sister. When the sister turns on him, he raises his voice at her, and Cam snaps at him and the two leave for lunch while Cam comments that he needs to calm down.
Black Books has a half-dying Bernard (having had to look after himself for a whole day) snap out of it when he hears that Manny is being bullied by his new boss. "HowDAREyou? Don't you touch a hair on that boy's head! Have you no respect? He's mine! Get your own human plaything, you quartz-brained little cream puff!"
On Home Improvement, Brad and Randy say that anyone who calls Mark a dork for wearing glasses will have to answer to them, because they are the only ones allowed to call him a dork.
In the pilot episode of The Inspector Lynley Mysteries, the fiery, sarcastic Detective Sergeant Havers - who doesn't even like her partner DI Lynley at this point - immediately takes offense at the accusations leveled against him by an old partner of Lynley's, with whom he had parted on rather unfriendly terms. And she does this while conveniently ignoring the fact that, just hours earlier, she had been levelling those same accusations at him! This proves to be an excellent indicator of their future relationship.
Friends: Occassionally Monica about Chandler. Like when they're having photo's taken.
Monica: "Chandler what is wrong with your face? It's meant to say Geller and Bing to be married, not local woman saves drowning moron!"
Monica: "Hey! Don't laugh at him, he's my drowning moron."
In Absolutely Fabulous Edwina and Patsy constantly belittle Edwina's daughter Saffron. Patsy goes as far as wishing Edwina had an abortion. But Edwina is often a bitch to Saffy. however when Saffy revealed that the man who was coming onto her was married and she didn't want his attention. Edwina decked the man and yelled "STAY AWAY FROM MY DAUGHTER"
Sherlock:[To Mrs Hudson] Though do, in fact, shut up.
In the Scrubs episdode "My New Suit", Dr Cox and Dr Kelso have a brief moment of camaraderie, and then Kelso hates Cox more than ever. Dr Cox can't understand what happened.
Cox: All I remember is we were both making fun of our kids, and bam, he stuck me with Ted.
Jordan: No, you made fun of your kid, he made fun of his kid ... and then you made fun of his kid.
Also, while Cox is always insulting and belittling JD and Elliot, he smacks down any strangers who try to do the same thing, and consistently defends them against Kelso. However, he doesn't care when their other superiors torment them (or in JD's case, the Janitor).
In Community, Jeff declares that "Greendale is our toilet, and no one craps in it but us!" at one point to get the rest of the study group riled up to save the day. Also, the study group declaring Britta "the worst" or otherwise making fun of her is very common, but when Mr. Rad, the glee club teacher, yells it at her, the entire group snaps out of their gleeful musical haze to defend her.
Troy: You do not get to call Britta the worst!
Buffy the Vampire Slayer: In the episode "Triangle" Willow and Anya have been constantly arguing, until they must unite to defeat a troll released by Willow's spell gone awry.
Willow: I have faith in you, Anya. There is NOBODY you cannot piss off.
An old strip of Garfield had Garfield smack into next week a cat that beat up on Odie, claiming "No one beats up Odie but me!"
In an early strip of For Better or for Worse, Michael roughs up a friend of his who made Elizabeth cry, saying, "No one makes my baby sister cry except me!"
Inverted: When Beetle Bailey hears that Sergeant Snorkel has beaten up a private from another company, he becomes outraged and tries to report him for infidelity.
In Fire Emblem The Sacred Stones, Colm repeatedly tells his childhood best friend she's useless and getting in the way on the battlefield, causing her to cry. Which is something nobody else is allowed to do, only he is allowed to make her cry.
In Costume Quest, your character doesn't exactly agree that their twin is their best friend. But when that twin is kidnapped by monsters, you go straight after them (admittedly, part of that is not wanting to be grounded), and at one point declare that your sibling is, while smelly, annoying, and wearing an embarrassing costume, "mine to terrorize, not yours!"
Portal 2 has GlaDOS frequently calling Chell fat and mocking on the fact that she seems to be an orphan - but when they team up against Wheatley and he uses the same insults, GlaDOS responds with: "What exactly is wrong with being adopted? [...] Also, look at her you moron. She's not fat." Subverted a few seconds later when she whispers to Chell that she is adopted and that's terrible, and that she's only defending Chell to annoy Wheatley, because his insults, while technically the same thing, are just crude compared to hers - "Fatty Fatty No Parents".
When Pram tries bullying Mickey in Makai Kingdom, Volvagia's two other heads quickly butt in and defend him, noting that the only people who get to bully Mickey are them.
Most of the core cast of Something Positive do this at some point, especially Davan, Aubrey and PeeJee.
El Goonish Shive: Ellen's typical approach to Elliot, largely because she used to 'be' Elliot. Elliot actually feels worse when Ellen doesn't tease him because he counts on it to help him through the craziness that has taken over his life (as in "It can't be that bad if we're joking about it.")
South Park: Shelley agrees to protect Stan and his friends from Trent Boyette, claiming that "no juvenile hall turd is going to kill you, that's my job."
Ben 10: "You can't treat my cousin like that!" "Thanks." "Only I can treat my cousin like that!"
In Ed Edd N Eddys Big Picture Show, the Kanker Sisters drag Eddy's brother into his trailer to give him some of their infamous attention for beating the crap out of the Eds. They were also outright disgusted at him for beating on them in the first place.
Throughout most of the film, the Kankers were hunting down and capturing the others kids for having the temerity to even try and harm the Eds.
Marie: Ain't no one beating up on my man but me!
In Hey Arnold, we have the Pataki sisters. Helga may not always like her sister Olga and take some pleasure in her sufferings at times, but when push comes to shove Helga will protect her big sister.
And, of course, Homer Simpson once told a bunch of rampaging robots "Nobody ruins my vacation except me! And maybe the boy!"
One moment in Dexters Laboratory, when a gang of villains smashes inside of a mall and a small piece of debris bounces off Dee Dee's head, mildly distracting her.
Dexter: Huh? Nobody clonks my sister but me!
(Dexter promptly dispatches the mooks with his superhero gear)
My Little Pony: Friendship Is Magic: Fluttershy's pet rabbit Angel frequently mistreats her, but he's there to slam the door on the Crusaders when their gossip makes her cry in "Ponyville Confidential".
In the Adventure Time episode "It Came from the Nightosphere", Ice King gets mad when he sees Marceline's father sucking the souls out of his penguin minions: "No one sucks the life from my penguins but me! And maybe polar bears, because that's just nature, Gunther."
Pete on Goof Troop generally treats his son PJ very badly and shows almost no concern for him outside of what he perceives to be life-or-death situations. However, in a few episodes, he also gets really mad when someone else attacks him, humiliates him, or drags him into doing something.
There are cases where if you bully someone's little sibling and the older sibling, however abusive he and she is, gets wind of it, they will beat the living crap out of you. Often saying that "Only I'm allowed to beat up/insult her/him."
This is a staple of US military culture, particularly among the Infantry. Soldiers who have served together, particularly in combat, have insulting nicknames for each other and sling profanities at each other like it's going out of style, no matter how grossly offensive the terms can be (and some of these can get pretty bad). Add to that that many of these insults back and forth will be meant sincerely, rather than in jest, but just the same they will tend to form a unified front against outsiders, just as the different branches will (usually) put their differences aside to work together against a foreign foe God help any outsider who tries the same thing, especially if they're from the Navy.
Some psychological studies suggest that male characteristics most correlated with bullying are also correlated with a very strong sense of group loyalty. Which means that it may be biologically ingrained for men to be bullies, even toward members of their own group, but also be the first to defend members of their group against anyone else.
N-Word Privileges are based around this. It's okay to make fun of a group as long as you are part of it. A person foreign to that group? Better watch his back.