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 punches 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.
Fridge Brilliance: Rin acts that way because of how different her and Kagura are. Both have bad tempers, but Kagura does not know her own strength and frequently hurts others when riled up. Rin knows that she isn't a serious danger to Tohru, but she can't trust Kagura to have the same discipline.
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 Himself 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 ˝: 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.
Kei: Why did you help me back there? 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 Freeza saga, and the early stages of the Main Buu saga.
There's also one instance right after the Namek arc, when Chi Chi hires a tutor for Gohan. This tutor happens to be quite abusive towards Gohan, and when he starts calling Goku a delinquent absentee parent (Goku is missing following the fight with Frieza) Chi Chi decides she's had enough and promptly defenestrates the tutor.
Natsu and Gray from Fairy Tail start off as rivals, but when Gray becomes The Lancer of the Five-Man Band they still fight all the time, unless someone else is threatening them, then they forget their squabbles and unify against whoever it is. Once Gray calms down somewhat, Natsu starts doing this with Gajeel.
In one episode of Yu-Gi-Oh! GX, Professor Chronos vehemently defends the Osiris Dorm from Napoleon, and then chews him out thoroughly for insulting them, yelling, "I'M the only one who gets to call these worthless students worthless!" (Of course, this was likely the point where he went from a reluctant ally of the protagonists to a full-fledged one.)
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.
Throughout most of the Fantastic Four's history, the Thing was harassed and teased by his former gang on Yancy Street who tended to call him a "sell out"; however, they often helped him and the rest of his team if a villain was giving them trouble on their turf, claiming "that's our job" on such occasions. (They really didn't mean it, anyway.)
The Marvel Universe crossover Maximum Security featured US Agent, now working for a Cape Busters force called S.T.A.R.S., co-opting The Avengers and being his usual abrasive self, utterly contemptuous of these so-called heroes. At the end, when he rejects Cap's offer of friendship, one of his S.T.A.R.S. colleagues says "You told 'em, sir. Who do they think they are?" and gets slammed against the side of their aircraft. You do not talk like that about the Avengers to US Agent.
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.
Mentioned in the South Park fanfic "How Cartman Stole Christmas".
Kyle was his to torment and his alone.
Arthur is often rude to Merlin in The Student Prince, but he gets protective when Lady Viva acts rudely to Merlin, promptly turning her down and shutting her out of their room.
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 one of the corrupt weapons dealers who sabotaged the pilots' planes.
Benson:You risked the lives of some damn fine pilots... and 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.
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!note 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.
Tywin Lannister and Walder Frey don't seem to have any sincere affection for their offspring, dealing out backhanded compliments and outright belittlement at every opportunity, but both of them will respond with utter ruthlessness to any outsider that dares slight a member of their families.
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 one episode of Clarissa Explains It All, Ferguson becomes a victim of the school bully, and Clarissa stands up for him saying, "He's my brother. If anyone's going to clobber him, it's going to be me!"
In another episode, Ferguson gets a new rich friend who Clarissa discovers is her secret admirer and is only using Ferguson to get to her. When trying to figure out how to tell Ferguson gently, Clarissa declares, "I don't want him crushed, only slightly dented!"
Megan does this on two occasions in Drake & Josh. In the first, she helps acquit Drake of a prank he didn't commit, and when Drake asks why she's helping him, Megan replies, "Because you're my brother, and I can tell you're sad and scared and upset, and I can't stand to see you that way...unless I cause it." In the second, Megan initially didn't like Mindy before she became Josh's girlfriend because she made him miserable...and that's Megan's job.
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.
On Cheers, Harry the Hat showed up frequently to swindle money out of the patrons and staff of the bar, but at times, he helped them out, partly out of sentiment, and partly to protect them from operators and crooks even more unscrupulous than himself, noting "I don't like the idea of someone else plucking my pigeons."
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!
Jeff may dislike the Dean but he took action after finding out he'd been kidnapped
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.
Vicious: In the finalé, Freddie ceases insulting his partner, Stuart, to stand up for him and admit his love for him when Stuart comes out to his mother and she turns on him. The niceness between them lasts all of thirty seconds:
Stuart: Did Freddie Thornhill just use the word love? Freddie: You're so desperate, clinging to every kind word tossed you way. It's very unattractive, Stuart, so why don't you get us some drinks, and stop standing there with your mouth gaping open like a cheap Italian fountain?!
Reese in Malcolm in the Middle mocks and beats up Malcolm and bullies Dewey all the time, but if anyone else calls them names or tries to pick on them, he takes it as his duty to kick the offender's ass in retaliation.
Subverted in Game of Thrones by Tywin Lannister. He despises his son Tyrion yet refuses to tolerate anyone else mocking or harming him. This has nothing to do with Tyrion and everything to do with the fact that anyone who wrongs him is defying the power and authority of House Lannister, which Tywin will not allow.
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.
In Dragon Age II, Carver's dislike of magic is due to an inferiority complex due to being a Muggle Born of Mages, which doesn't help his rivalry with his elder sibling if they are also a Mage. That said, when Fenris insults Mage Hawke by claiming that Mages are alwayspower-hungry, a furious Carver quickly steps in to defend their sibling.
In Batman: Arkham City, The Joker berates Batman for beating up Harley Quinn, only to state that it's his hobby.
The titular hero displays this behavior in the Rance h-game series. Rance will bully his slave girl Sill Plain from dawn 'till dusk and take liberties with just about every woman he meets, but if you hurt a woman "for real" when he's anywhere nearby, nothing that exists will save you from his Unstoppable Rage.
a2 ~a due~: One of the orchestra members has a moment of this for Hao, as he helps protect both Hao and Sona from a bunch of thugs.
Percussion player: The only one who can make fun of our conductor is me!
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.")
Spiderman: Wow. Supes must mean a lot to you for you to go all this trouble to find him. Batman: 'Supes' is a headstrong, naive idiot without the least bit of common sense for these situations. (Spiderman laughs) Batman: But only I'm allowed to say that. Spiderman: (meekly) Yes sir.
Parody Janeway from SF Debris has a simple rule: Only she gets to make the lives of her crew a living hell. Anyone else trying to get in on it is in serious trouble, except possibly Neelix and that's because she gets to torment him too.
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 Eddy's 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.
In Rocket Power, Lars doesn't like it when his cronies insult Twister. Only he can do that. It's a brother thing.
The Simpsons: Bart and Lisa Simpson have occasionally invoked this when anyone else goes after the other.
And, of course, Homer Simpson once told a bunch of rampaging robots "Nobody ruins my vacation except me! And maybe the boy!"
A truly demented version occurs during a Halloween Episode where Bart and Lisa are drawn into an Itchy and Scratchy cartoon due to a plutonium-powered TV-remote. They watch Itchy pull his lethal, gory assault on Scratchy, as always, and then laugh at it... But this time, the cartoon duo can hear them, and Itchy thinks they're being mean. Scratchy pulls himself together, and the two decide to teach Bart and Lisa a lesson, violent cartoon style, requiring them to run for their lives!
One moment in Dexter's 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.
This goes double for any military instructors, no matter how nasty they are. A guy like this will intimidate and insult the troops he trains with dirty language - because that's his job, frankly - but if anyone else insults his men, he shows that guy how nasty he really can be.
It's the same way with most sports teams. Team members can make fun of each other, but if another team insults your teammates...
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.
This type of phenomenon exists between Swedes and Finns, Swedes and Norwegians and Norwegians and Danes.
Americans are allowed to make fun of Canadians. And only Americans. (At least, as far as the Americans are concerned.)