Beware the Nice Ones

"You might have everyone else here buying your ... 'transformation', but you and I both know you've struggled with doing the right thing in the past. So let me tell you something right now: you make one step backward, one slip-up, give me one reason to think you might hurt Aang and you won't have to worry about your destiny anymore, because I'll make sure your destiny ends, right then and there; permanently!"

- Katara threatening to take Zuko's life if he shows any sign of treachery or harming Aang.

Beware the Nice Ones is a term that is used in hero-related media. Good guys are well-known of their personalities, traits and actions. However, in works of fiction, or real life, when villains push these characters too far, by having their friends, family or even homeland threatened, he or she might get extremely angry and want to destroy their enemies for their cruelty. This action manifests usually with the hero losing every bit of control and composure he/she had after their allies or community is threatened: glowing in fury and/or throwing a huge tantrum. It can also manifest as a murderous fit of rage or even a large sense of fear may contribute to them frightening their provoker.

It must be noted that in many cases, the kind-hearted guys who can get angered quickly when provoked are "Gentle Giants" with immense conscience, and an good heart to match, who cannot stand to see their buddies and homeland in danger.

Anime & Manga

 * Goku (Dragonball) (even when fighting seriously to avenge fallen comrades or save the world) maintains a constant kind disposition and childlike naïveté throughout the series, allowing for humour in otherwise climactic battles. However, Goku only completely snaps when Frieza mercilessly kills his lifelong best friend Krillin and threatens to kill his son. His first transformation into a Super Saiyan turns him into a cold, taunting, ruthless and arrogant fighter who starts to beat Frieza to within an inch of his life.
 * Gohan (Dragon Ball Z) is a pacifist who abhors violence, but when provoked (namely by hurting his precious people, or just any Innocent Bystander for that matter), can fly into a near psychotic rage and suddenly increase his strength to colossal heights.
 * Captain Retsu Unohana (Bleach) is a motherly Yamato Nadeshiko type in charge of a company full of healers, but one look from her can scare anyone, even people who don't scare easily such as Kenpachi Zaraki.
 * Hanji Zoe (Attack on Titan) comes across as extremely cheerful and eccentric, being one of the most friendly senior officers in the Survey Corps. However, Hange shows no mercy once provoked — dangling a priest 50 meters off the ground to interrogate him and on another occasion, calmly preparing to engage in a bit of cold-blooded torture against a captured enemy.
 * Hungary (Hetalia) is the cute young girl who was Austria's maid and later advisor before marrying him, but she will not hesitate to invoke her massive fighting skills (which she acquired when she was a pint-sized warrior girl) and attack if anyone hurts her husband.
 * Alphonse Elric (Fullmetal Alchemist) is a Gentle Giant who is very good-natured, but he has come close to flying into a merciless rage (and does a few times in the first anime) on multiple occasions, even after anyone messes with those he cares about.
 * Gon Freecss (Hunter × Hunter) is a cute, lovable and friendly guy...unless anyone does anything to hurt or threaten any of his companions.
 * Naruto Uzumaki (Naruto) is an good-hearted and noble person (who refused to give in to his emotions and extract vengeance upon the man who just killed both of his teachers and leveled his village with the ground, in order to break the chain of hatred) has a malevolent, nine-tailed demon fox of immeasurable power sealed into himself—and this fox's power has a habit of seeping out of him whenever he loses his temper.
 * Kurama from Yu Yu Hakusho was the embodiment of this concept; Polite, generous, empathetic,...merciless and creatively sadistic.
 * Kagome Higurashi (Inuyasha) is easily the kindest, sweetest and most helpful and compassionate character in the entire series and seemingly unable to turn her back on anyone in danger, but after seeing Naraku's despicable methods of turning Sango and Kohaku against each other, she nearly killed him out of rage and contempt, saying she wouldn't let him go even if he begged for forgiveness. Even Inuyasha was startled by her anger.
 * Mika Jougasaki (The iDOLM@STER: Cinderella Girls) is kindhearted, encouraging, and caring, but when the Producer loses her sister Rika in a big city, she berates him, but the Producer is able to calm her down and help her find her sister.
 * Lockon Stratos/Neil Dylandy ( Mobile Suit Gundam 00) : is the most mature, kindhearted, level-headed, calm, and easy-going meisters. But after he faced his family killers, Ali al-Saachez, he become very-dark, brutal, and ignore the warn from his comrade about his condition, which he become thirst for revenge his family death.

​Live Action Film

 * Glen Ray (Child's Play 5: Seed of Chucky) is not like his family who enjoys killing, as he doesn't. On the other hand, he deliberately kills his father Chucky for having killed the former's mother Tiffany, much to Chucky's own shock and pride, but also to the depression of Glen himself.
 * Jess Aarons (Bridge to Terabithia) is a nice kid, who is otherwise never aggressive but after his friend Leslie dies, and a bully makes a joke about it, Jess punches the bully across the room without warning.
 * Caesar (Planet of the Apes) is a wise and kind ruler of the apes, but it should be noted he led the initial rebellion against the humans that earned the apes their freedom. Even as the ruler of the apes, he can be dangerous. When the treacherous ape Koba accuses him of loving humans more than his own sons, Caesar inflicts a beating on Koba. When Koba became a tyrantical ruler, and killed humans and other apes, Caesar decided it was perfectly reasonable to kill him.

Animated Film

 * Sid (Ice Age)
 * Donkey
 * Mater: This goofy unloving tow truck may look like an idiot but he is definitely smarter than he looks as proven in the sequel where he exposes the villains plan to sabotage the racer's oil.

Western Animation

 * Bubbles (Powerpuff Girls) is the joy and laughter, and she is the sweetest of the three Powerpuff Girls.
 * Beast Boy is the comic relief of the Teen Titans and a genuinely nice guy. However if you threaten his friends or break his heart, he becomes much more serious and fight to the bitter end.
 * Aang (Avatar: The Last Airbender) is an kind-hearted, generous and pacifistic monk who loves animals and world peace, especially his friends. However, when provoked, his eyes start glowing and he becomes a demigod capable of throwing hurricanes, tidal waves and mountain ranges around like softballs. He is so terrifyingly powerful and destructive he terrifies his enemies, innocent bystanders and even his allies.
 * Similarly Avatar: The Last Airbender also gives up Uncle Iroh. He did not get the nick-name "Dragon of the west" for his tea recipes. Even while writing a letter about his imminent conquest of the Earth Kingdom capital he seems more like a chatty uncle causally mentioning his hobbies than a feared war-lord.
 * Maggie Simpson of The Simpsons may just be a baby who appears to be completely passive and sweet, but she has proven time after time that she is not to be trifled with, she is freakishly talented with knives and fire-arms.
 * Princess Bubblegum (Adventure Time) is the benevolent princess in all of the Candy Kingdom. However, when her allies are threatened, she will become enraged that she fights in a harsh manner.
 * Francine Smith (American Dad!) is a polite lady who can snap in a rather disturbing manner when provoked.
 * Droopy Dog (Droopy Dog cartoons) is a stoic and monotone character unfazed by any problem. However, if anyone do something truly petty in cruelty (especially to "The Dame"), he will walk up to that person and note in the same monotone, "you know what? That makes me mad." Then he proceeds to demolish them with the same dispassion as before.
 * Ben Tennyson (Ben 10) is a kind-hearted, outgoing guy (though a bit egocentric and foolish at times), but if anyone push him too far (such as, put his girlfriend's life at risk just to spite him, destroying his favorite alien form or harm his friends), he will get extremely angry and beat up his provoker.
 * Numbah 3 (Codename: Kids Next Door) is the team's sweet ditzy girl, but when she does get angry, she will engage in battle in a ruthless manner.
 * Dukey (Johnny Test) can battle in a ruthless manner when pushed too far.
 * Ron Stoppable (Kim Possible) is a generic goofy sidekick that mostly gladly acts as a distraction, but if anyone get him angered by either hurting Kim or boasting about destroying Bueno Nacho he gets in such a rage that he will attack.

Video Games

 * Amy Rose - she appears to be a sweet, cheerful girl hedgehog, but when something provokes her, she will pull out her Piko-Piko hammer and attack.
 * Sheogorath of the Elder Scroll series loves to play this. He is kooky, friendly and charismatic; That being said when you get to talk to him face to face in Elder Scrolls IV: Oblivion: The Shiverin Isles, attack him, go on we dare you, see what happens.
 * The Boss of Saints Row is a very light-hearted gang leader, his/her main goal in life is to have a good time with few to no caveats attached. He/She likes to get high, attend strip clubs, treat his/her friends to parties and will greet any rivals as potential allies until they prove otherwise. But for the love of all that is holy DO NOT give, him/her back-talk or hurt one of his/her friends!

Literature

 * Skulduggery Pleasant is a suave, good hearted sorcerer that cares with his friends despite his egoistic side. However, he will become a deadly opponent if any of them is hurt by other villains since Nefarian once sadistically slaughter his entire family and he tries to kill him (but fails as Nefarian power turned out sabotaged so Skulduggery survives). To make matter worse, those events drove him developed a dissociative personality disorder where should enraged enough, his second personality, Lord Vile, will took over his mind and his rage likely last long.
 * Samwise Gamgee of J.R.R. Tolkien's Lord of The Rings trilogy is very timid, honest and selfless, but he will charge straight into death with a fire in his heart, ready to take on anything that gets in his way if his friend, Frodo, is in trouble.

Theology

 * The Shinto goddess Izanami was a reserved, nurturing, humble goddess who helped form Japan and died while giving birth to her divine offspring. When Izanami's husband, Izanagi, entered the underworld to retrieve her she was appalled that he would break sacred tenants to enter the Underworld and flew into a rage trying to destroy him. Though Izanagi escaped and sealed the entrance he had used, Izanami vowed to drag thousands of the souls of his mortal worshipers into the afterlife a day to pay him back.
 * Zeus was a very laid-back god. He rarely took anything seriously and was even willing to allow mortals to openly mock him provided there was no true malice behind their words, he was even considered the paragon of Greece's concept of being a charitable host. But even with his easy-going demeanor and legendary charisma there is a very good reason he codifies the term "Smite".