Some classic {{Archetypal Character}}s or characters with a trope associated with them who might be the cause of this:
* The ActualPacifist starts a fight.
* An AffablyEvil villain drops all signs of niceness entirely, particularly during a VillainousBreakdown.
* The AffectionHatingKid wants a hug or doesn't mind seeing people hug.
* TheAlcoholic[=/=]HardDrinkingPartyGirl puts down their drink for the time being (or dumps it out and [[NoMoreForMe swears to never drink again]]).
* The AllLovingHero [[EvenTheLovingHeroHasHatedOnes wants to hurt/kill someone]].
* The AloofBigBrother is suddenly nice to their younger sibling(s).
* The AlphaBitch doesn't antagonize anyone, including their usual targets.
* The AnimalLover acts mean towards an animal, or even wishes death on one.
* The AnnoyingYoungerSibling isn't acting obnoxious or rude to their older sibling(s).
* The AntiHero decides not to do their common anti-heroic trait.
* The ApatheticTeacher becomes more engaged with their student(s).
* The ApologeticAttacker offers no form of apology and/or regret from hurting someone.
* An ArrogantKungFuGuy acts humble or meets an opponent they state is better than them.
* Someone with AttentionDeficitOohShiny stays focused on the task at hand.
* An AttentionWhore doesn't want to be the center of attention or doesn't notice when they are.
* An AxCrazy person is both calm and doesn't want to get violent.
* The BadBoss doesn't harm or threaten to harm their underlings. Double points if they do something [[PetTheDog nice]] for them.
* The BenevolentBoss is unusually mean to their employees.
* Anyone with a notable BerserkButton don't react with the usual anger when the button is pressed.
* TheBerserker[=/=]HotBlooded guy calms down, or goes into TranquilFury.
* The BestFriend antagonizes their best friend or acts like they don't know them.
* The BigBrotherBully doesn't antagonize their younger sibling(s).
* Someone who has a BigBrotherInstinct doesn't step in to defend and/or protect their younger sibling(s).
* The BigEater states that they're not hungry, double points if they turned down their TrademarkFavoriteFood.
* The BitchInSheepsClothing is genuine about their kindness with no ulterior motives.
* The BloodKnight suggests a peaceful solution or is repelled by violence.
* Someone with BlueAndOrangeMorality conforms to normal standards of morality.
* TheBore does something interesting.
* The BrattyHalfPint is genuinely polite and well-mannered.
* TheBully doesn't target and/or is nice to their victim(s).
* When there's ABoyAndHisX, the boy or the X starts acting strangely towards their respective buddy.
* TheCasanova, the LovableSexManiac, the GoodBadGirl, the person who ReallyGetsAround, or the ChivalrousPervert shows disinterest in sex/romance.
* Somebody with a catchphrase doesn't say it at a time when they ordinarily would or [[SubvertedCatchphrase says something else instead of their catchphrase]] (sometimes even [[SelfBotchedCatchPhrase seeming like they're trying to say it but they can't]]) at a time when they'd usually say their catchphrase, or [[AlternateCatchphraseInflection says their catchphrase in a different tone of voice from usual]]. Alternatively, someone (who may or may not have one themselves) [[BorrowedCatchphrase says somebody else's catchphrase]].
* TheChessmaster makes use of the IndyPloy.
* The ClingyJealousGirl, CrazyJealousGuy or {{Yandere}} doesn't act out when someone makes moves on their love interest.
* The ClockKing or the CreatureOfHabit deviates from their routines ''purposely''.
* The CloudCuckoolander begins to talk and/or act logically.
* A ComicallySerious person tells jokes or laughs at someone else's.
* TheConfidant doesn't want to give advice or gives bad advice.
* The CombatSadomasochist tries to defeat their opponent quickly and takes no joy in it.
* The ConsummateLiar is unable to hide the truth from someone.
* The ControlFreak doesn't want to be in control or wants to be chaotic.
* A CoolBigBro starts acting more [[AloofBigBrother cold]] or even [[BigBrotherBully mean]] to a younger sibling.
* The CoolMask wearer suddenly [[TheReveal removes it]]; one normally in makeup being without also fits this.
* The CoolTeacher lacks interest in teaching their student(s).
* The CuddleBug or person with NoSenseOfPersonalSpace respects someone's personal space.
* TheCynic starts to be optimistic.
* The DaddysGirl is distant with her father. Double points if she is either angry or disrespectful with him.
* The DeadpanSnarker [[SarcasmFailure is at a loss for words]].
* The {{Determinator}} gives up.
* The DirtyCop does their job professionally.
* A DirtyCoward[=/=]LovableCoward stands up to fight.
* A practitioner of DissonantSerenity loses their cool.
* TheDitz does something distinctly [[SmartBall intelligent]] and/or sensible.
* A character who DoesntLikeGuns [[BatmanGrabsAGun uses one]].
* Someone with a DrinkBasedCharacterization chooses not to have their favorite drink.
* TheEeyore becomes genuinely happy and behaves accordingly.
* One whose [[EyesAlwaysShut eyes are always shut]] opens their eyes, even if only for a second.
* The ExtremeDoormat [[GrewASpine stands up for themselves]].
* The FearlessFool becomes scared or admits something is too dangerous.
* TheFettered or TheUnfettered compromises on their ideal or goal.
* The FriendToAllChildren starts being mean to children or believes a child is [[EnfantTerrible too dangerous]] to keep around.
* Creatures stop liking, or even become scared of, someone who's usually a FriendToAllLivingThings.
* TheFundamentalist thinks [[EveryoneHasStandards someone on their own side is too extreme]]. Bonus if it's BigBad and/or TheHeartless one [[EvenEvilHasStandards being disgusted]].
* TheGadfly doesn't make fun of anyone but is completely serious.
* The GenkiGirl becomes quiet and/or reserved.
* [[TerrifiedOfGerms The germophobe]] goes somewhere or touches something filthy.
* The GloryHound or GlorySeeker lets someone else take the credit.
* The GoshDangItToHeck person [[PrecisionFStrike swears for real]].
* The GracefulLoser takes a loss [[SoreLoser poorly]].
* The one with a GuiltComplex refuses to take responsibility for their actions or accepts that they are not at fault.
* The character with a HairTriggerTemper waves off a slight. Double points if they didn't react to, or even [[ActuallyPrettyFunny laughed at, their]] biggest BerserkButton.
* The character who HatesBeingTouched allows someone to touch them (almost always in the form of [[SecurityCling a hug]]).
* The HeavySleeper is awakened by something that wouldn't normally wake them up.
* The HeroWorshipper turns against their hero.
* The IndyPloy practitioner actually takes time to plan things out.
* The IneffectualLoner asks for assistance.
* The InsufferableGenius admits they don't know/are not smart enough to figure out something.
* The ItsAllAboutMe or [[MoralMyopia Morally Myopic]] person shows concern for others, however grudgingly; the former tries to avoid the spotlight.
* A person who normally engages in JackBauerInterrogationTechnique does not use torture on a person.
* The {{Jerkass}} [[TookALevelInKindness becomes very kind]].
* The JerkJock commits a [[PetTheDog genuine act of kindness]]. Double points if they do this towards their usual bully target.
* A {{Keet}} becomes subdued.
* The KnightTemplar is horrified/ashamed by their actions.
* The KnightTemplarBigBrother refuses to harm someone who hurt their sibling(s).
* The KnightTemplarParent doesn't harm someone who hurt their child(ren).
* A LargeHam tones it down.
* A LazyBum or {{Sleepyhead}} becomes active.
* The LeeroyJenkins becomes extremely cautious.
* Somebody with a LimitedWardrobe wears different clothes for no reason.
* The LovableJock acts mean towards those they are usually nice with.
* The LovableTraitor doesn't betray their allies.
* A ManChild acts mature.
* The MasterOfTheMixedMessage is completely honest about their feelings, with no room for doubt.
* The MeanBoss does and/or says something nice to their employees.
* The MellowFellow becomes stressed and/or angry.
* The MommasBoy is distant, angry, or disrespectful with his mother.
* The MotorMouth shuts up.
* The {{Narcissist}} is either humbler than usual, shows empathy to someone else, or doesn't care for the attention he's given.
* Someone with NervesOfSteel or TranquilFury loses their cool or even goes into UnstoppableRage.
* The NeatFreak doesn't clean up or doesn't care that something is dirty.
* The NervousWreck turns into a daredevil.
* Someone who is NeverBareheaded is seen without their trademark hat.
* The NeverMyFault person admits ItsAllMyFault.
* The NiceGuy [[TookALevelInJerkass takes a level in Jerkass]].
* TheNicknamer calls another character [[YouCalledMeXItMustBeSerious by their real name]].
* The person with NoIndoorVoice whispers.
* The NonActionGuy gets into a fight. Double points if they're the one who ''started'' it.
* The NotSoOmniscientCouncilOfBickering manages to act quickly and decisively. Bonus points if their decision is unanimous.
* The OmnicidalManiac tells someone that YouWillBeSpared.
* Children stop hanging around someone who's normally OneOfTheKids.
* The OnlySaneMan acts wacky.
* The BoyfriendBlockingDad doesn't react when their child states they are dating someone.
* The PerfectPacifistPeople rise up in arms.
* The PerpetualFrowner stops frowning [[TheUnsmile and]] [[TechnicallyASmile /or]] [[SlasherSmile starts]] [[WhenSheSmiles smiling]]...
* The PerpetualSmiler stops smiling and/or starts frowning.
* The PickyEater eats [[DoesNotLikeSpam a food they hate the most]], and starts liking it.
* ThePigPen cleans up.
* The PluckyComicRelief becomes dead serious.
* The PoliticallyIncorrectHero or [[PoliticallyIncorrectVillain Villain]] doesn't say anything bigoted about whichever group they are prejudice against. Take it a step further if they willingly partner with someone from said group with no complaint.
* ThePollyanna admits to despair.
* A character who PrefersGoingBarefoot begins wearing shoes all the time.
* The ProfessionalButtKisser doesn't take the opportunity to get in their superior's good graces. Double points if they either act more disrespectful to said superiors, disobey an order, or don't even notice when said superior praises them.
* The ProperLady [[PrecisionFStrike speaks]] or acts improperly.
* The ProudWarriorRaceGuy says a plan of action is too dangerous.
* The PushoverParents discipline their child(ren).
* TheQuietOne begins to talk more frequently.
* The ReasonableAuthorityFigure starts acting obstructive to their team.
* TheReliableOne states that they can't help someone in need.
* The ReluctantFanserviceGirl lets loose or is unbothered by her nudity.
* Someone who dishes out RhymesOnADime stops rhyming.
* TheScrooge suddenly gives something away.
* Someone who speaks in SesquipedalianLoquaciousness doesn't use big words or can't pronounce a big word.
* The ShamelessFanserviceGirl dresses conservatively, and not for health reasons, or has a NakedFreakOut when stripped.
* The ShipperOnDeck is uninterested in how their favorite couple(s) are having a romantic moment together.
* The ShrinkingViolet[=/=]ProneToTears character becomes confident.
* SirSwearsALot doesn't drop even a single, mild swear.
* TheSlacker is proactive.
* TheSleepless falls asleep, acts sleepy, or claims to be tired.
* The SmugSnake loses all of his/her haughtiness and becomes ashamed of him/herself.
* TheSocialDarwinist forgoes their philosophy.
* The SociopathicHero expresses genuine concern to others, self-shame, or compassion.
* The SoreLoser takes a loss [[GracefulLoser surprisingly well]].
* TheStoic becomes NotSoStoic.
* The StrawCharacter demonstrates actual tact, respect for their opponent, and logic.
* The SugarAndIcePersonality or {{Tsundere}} is upfront about their affection for the love interest.
* The SupremeChef makes a food that nobody likes.
* TheTeetotaler drinks alcohol, double points if they claim they [[INeedAFreakingDrink needed it]].
* The TerseTalker speaks in ''complete sentences''.
* The ThirdPersonPerson uses a personal pronoun/refers to themselves in the first person.
* One of ThoseTwoGuys is seen without the other.
* One who practices ThouShaltNotKill takes a life.
* The TokenEvilTeammate performs or suggests a more heroic solution for a problem.
* The TokenGoodTeammate performs or suggests a more evil or morally dubious solution for a problem.
* Someone with a TrademarkFavoriteFood refuses their favorite snack and/or meal.
* The TricksterMentor clearly and directly tells their protege what they want.
* The {{Troll}} doesn't take the chance to drag someone down.
* The TrueCompanions don't get along.
* One who normally likes to TurnTheOtherCheek [[RejectedApology rejects someone's apology]], double points if they said to their offender on that what they did is [[ThisIsUnforgivable unforgivable.]]
* TheUnapologetic gives out a [[SincerityMode sincere, heartfelt apology.]]
* The UnderstandingBoyfriend isn't supportive to their partner.
* The character with UndyingLoyalty pays no attention to (or turns against) their master.
* The UngratefulBastard shows genuine gratitude for once.
* Someone with an UnlimitedWardrobe starts wearing only one pair of clothing.
* The one with a VerbalTic [[VerbalTicked speaks normally without dropping a single tic]].
* The ViolentlyProtectiveGirlfriend doesn't attack the person who hurt their lover. Double point, if the former is fighting ''against'' their latter.
* TheVoiceless or TheSilentBob [[SuddenlySpeaking talks]].
* The WalkingShirtlessScene puts on a shirt.
* The WellDoneSonGuy doesn't care that their action can lose their parental figure's respect.
* The character who bemoans WhyDidItHaveToBeSnakes doesn't react to one, even when it's right in front of their face, or even attacks it.
* The YouNoTakeCandle speaker talks with normal syntax.
* The ZanyScheme maker comes up with a sound and logical plan.
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