->''You know her by day\\
But you don't know Karen by night''
-->-- '''Jill Sobule''', "Karen by Night"

%% One quote is sufficient. Please place additional entries on the quotes tab.

Nina is a [[HotLibrarian librarian]]. During the day, she wears long skirts, a loose blouse done all the way up to her neck, her hair in a bun and sensible shoes.

Get Nina home to her significant other, allow her to have [[InVinoVeritas a glass of something alcoholic]] and well... the [[DressHitsFloor blouse is on the floor]], the skirt is in the hall and the [[LettingHerHairDown hair is all over the place]]. Some other stuff is {{NSFW}} even to describe...

A SubTrope of LivingADoubleLife.

Compare SeeminglyWholesomeFiftiesGirl.
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!!Examples:

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[[folder:Anime and Manga]]
* A [[{{Manga}} Hentai Manga]] take on this: ''[=WereSlut=]'' (unfortunate name [[CompletelyDifferentTitle created from whole cloth]] by Eros Comix, the US distributor) is about a shy college student named Kimiko who takes a magic beauty pill to make her attractive enough to win her childhood friend (read: [[HollywoodHomely she takes off her glasses]]). It works, but, due to the magic pill being past its expiration date, it keeps kicking in whenever she gets aroused. After the first time, though, it also kills all her inhibitions.
** Ditto for the manga/anime ''Sprite: Between Two Worlds'',wherein Manami, a severely repressed and meek college student turns into Nami, an outrageously uninhibited flirt whenever she's put into any situation that is too much for her to handle. The catalyst is her cousin Toru, who convinced Manami to be more confident around him when they were young by convincing her she was really Nami.
* In the {{ecchi}} manga ''MyBalls'', the main character's primary love interest Minayo is a sweet, kindly young woman who works at a daycare center. When she gets drunk, however, she goes into what the protagonist describes as "full-blown nympho mode". Unfortunately, said protagonist can't have sex for a month or the demon sealed inside his balls (hence the name of the manga) will be released and cause {{The End of the World As We Know It}}. Minayo happens to be an alcoholic, and HilarityEnsues.
* ''Anime/ParanoiaAgent'' has an episode that plays with this. Harumi Chono is a quiet, conservative, mild-mannered school teacher by day, but at night her [[SplitPersonality other personality]] takes over--Maria, a popular prostitute. When Harumi gets engaged, she starts to desperately get rid of Maria before her wedding day, which causes Maria to fight back.
* ''Anime/CodeGeass'''s [[HotScientist Nina]] [[MeaningfulName Einstein]] and the infamous [[CargoShip table scene]]. Nunnally actually ''walked in on this'', but fortunately she was blind already.
** And thank god, Nunnally's (''probably'') too young to properly...''interpret'' any sounds she might have heard.
*** Then again, said girl is [[WiseBeyondTheirYears Wise Beyond Her Years]]...
* ''{{Paprika}}'': Straight-laced Chiba becomes a lot more flirty and extroverted when she turns into [[spoiler: Paprika]].
* In a way Nyamo-sensei of ''Manga/AzumangaDaioh''. While she's generally straight-laced and down-to-earth in contrast to [[HardDrinkingPartyGirl Yukari]], the one who you'd expect to have a wild social life, Yukari makes a comment about her Nyamo "not being alone" in a previous summer, and RelaxoVision or not, the hilarious incident where she gets drunk and gives TheTalk implies she's fairly experienced.
* In the manga ''CrimsonSpell'' the protagonist is under a strange curse that causes him to turn into a [[HornyDevil Demon]] that can only be vanquished by being ''raped'' into submission. Conveniently he never has any memory of this the next day.
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[[folder:Comic Books]]
* While it never came up in the comics, writer Mark Waid's character notes for the ''ComicBook/FantasticFour'' speculate Susan Storm was like this as a young woman to cope with the stress of having to raise her little brother.
* Aurora was like this in ''ComicBook/AlphaFlight'''s early years, exaggerated by her SplitPersonality. One persona was Jeannie-Marie: strict, stuffy schoolmarm teaching at the same girls' school she was raised in. And then there was ''Aurora'': sultry, adventure-loving, free-spirited partier.
* In ''QuantumAndWoody'', Amy Fishbein appears to be a prim and proper white-collar professional, but she starts dropping {{Anvilicious}} innuendos and [[DressHitsFloor undressing herself]] as soon as she's alone with Woody.
-->"God, Woody, you didn't tell him about 'Cats', did you? It's not every girl who [[NoodleIncident loses her virginity in a Broadway show...]] I'll bet I can get us some tickets. ''Meeoww.''"
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[[folder:Fan Works]]
* In [[FanFic/APikachuInLove A Pikachu in Love]], Pikachu is worried that this is what Ash and Co. will think if they catch him sneaking off at night to meet Pichi, and doesn't want them drilling him for questions on the matter. [[spoiler: That still doesn't stop Misty from finding out, though she doesn't press the matter and keeps it a secret from the others even after the ending.]]
* More than one ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' fanfic has portrayed [[ShrinkingViolet Fluttershy]] like this.
** [[http://www.fimfiction.net/story/93809/1/a-pleasant-surprise/a-pleasant-surprise A Pleasant Surprise]] paints her as being quite assertive and forthcoming with her sexuality to the point of outright seducing the protagonist.
** [[http://www.fimfiction.net/story/100083/1/blissful-dream/blissful-dream Blissful Dream]] is another such story. Here, Fluttershy is shown as being sexually dominant over her lover.
** ''Fanfic/AdviceFromPinkiePie'' puts Fluttershy in a BDSM relationship - as the ''dominant'' one - with Rainbow Dash ("Now, my little pony… you're going to love me."), while in ''[[http://www.fimfiction.net/story/12708/my-little-slave My Little Slave]]'', [[spoiler: she initiates a rape-dungeon roleplay that lasts for 29 chapters before the reader finds out the truth]].
* Celestia, Luna, and Cadance all show this to varying degrees in ''FanFic/DiariesOfAMadman''.
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[[folder:Film]]
* The movie ''Film/BelleDeJour'' is about a seemingly average housewife who's a prostitute in secret. But here this trope is inverted: as she is a housewife, she can actually do this job only ''by day'' instead of by night. (This is where the name of the film comes from.)
* The [[HeroesWantRedHeads red-headed librarian]] from ''Film/{{Tomcats}}'' looks like a plain, uptight young lady. She (and her grandma!) are also into S&M.
* This is a source of some confusion in the film ''Film/DesperatelySeekingSusan''.
* Somewhat subverted in the film ''Film/BlindDate'' where Creator/BruceWillis' sister-in-law tells him not to let the date get drunk as she goes wild. This information is relayed to him via his brother who adds lots of leering to the information. Cue the man getting his date (Kim Basinger) drunk, to find that she goes wild in a drunk-driving, crash-the-car, ruin-the-evening way.
* ''Looking for Mr. Goodbar'' is a very dark example. Diane Keaton plays a teacher of deaf childen from a conservative Irish-Catholic upbringing who starts out having an affair with a married college professor, then starts cruising seedy bars for one-night stands that grow progressively more degrading and dangerous, culminating in her getting raped, beaten, and stabbed to death by a troubled Vietnam vet.
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[[folder:Literature]]
* The essence of ''TheStrangeCaseOfDrJekyllAndMrHyde''. Jekyll is an upstanding citizen by day, but he becomes Mister Hyde by night in order to live out his immoral, sadistic fantasies without being recognized.
* The ''Series/{{Torchwood}}'' novel ''[=SkyPoint=]'' takes this to extremes; a very prim and proper little old lady, who is actually an S&M prostitute.
* Almost every Cairheinan noblewoman in the ''WheelOfTime'' is heavily implied to fit this trope. Though during some festivals they will run around almost nude on the streets, especially during the Feast of Light (during which normal prohibitions against inter-class kissing (and other things) are lifted), leading to a large number of commoners having bragging contests about who made out with the most important noblewoman.
** ONLY during the Feast of Lights, after which any such incident is ignored by all parties. With Cairhien being partially based on Versailles France, this roughly corresponds to Mardi Gras.
* A relatively tame version occurs in ''Literature/GoodOmens''. Sweet little old lady and part-time medium Madame Tracy also offers appointments for "strict discipline and intimate massage every evening except Thursdays", and there are hints that she goes a little further than that on Thurdays.
* In ''Literature/SavingZoe'', Teresa is a pretty preppy girl who acts and sings. By night, she hangs out with drug dealers and porno producers. The same could be said about Zoe, who seems like a perfect bubbly girl but smokes drugs and has sex when her parents don't know. This tendency leads to Zoe's death.
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[[folder:Live Action TV]]
* ''OnTheBuses'' long-suffering Olive would love to be Naughty By Night, but her miserable husband Arthur would rather sleep. Actually, he'd probably rather do his taxes...
* Effy from ''{{Skins}}'': innocent schoolgirl by day, FilleFatale by night.
* Sheila from the US version of ''{{Shameless}}''. By day she's a sweet agoraphobic and germaphobic housewife. But at night she is very very into pegging filthy alcoholic Frank.
* ''Series/{{Angel}}us'' hints that cute geek girl Fred is like this.
-->"Ah, Fred. You look all fresh and sweet, but I hear you at night in your room with Gunn. The things you say. I'm lying there, listening, [[ADateWithRosiePalms hands under the covers... I can't help myself. It's so... gripping]].
* ''Series/TwinPeaks'' - Laura Palmer is a normal high school girl by day, but a prostitute at night, among other things. Or, as she says in Main/TheMovie, "Night time is my time."
* ''Series/{{Reno 911}}''. Deputy Weigel and her boyfriend Craig both appear to be socially-awkward nerds, but what we see of their sex life is quite... adventurous. Subverted in that [[spoiler: Craig turns out to be a serial killer]].
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[[folder:Theatre]]
* The play ''MissJulie'' fits this with regard to personality, but replace "librarian" with "aristocrat".
* Fantine in ''Theatre/LesMiserables'' is fired from her factory job when she is discovered to have a child, and her fellow workers claim that she is a prostitute. However, she had only ever had one lover, who had abandoned her, and it is only after she is fired that she has to become a prostitute.
* The song "Miss Byrd" from ''CloserThanEver'' is about a secretary exulting in how no one who sees her would think that she's anything but "that dull Miss Byrd," yet she has secret trysts with her superintendent.
* Parodied in ''TheMusicMan'': The town gossips manage to convince the Professor that [[HotLibrarian Marian the Librarian]] is NaughtyByNight primarily because she reads "racy" books by "Chaucer...Rabelais...Balzac" and was kind enough to befriend the town outcast. She's not, but he falls in love with her anyway.
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[[folder:Music]]
* the Music/GoodCharlotte song ''Like it's her Birthday'' has this as the main theme - the Protagonist thinks his Girlfriend's cheating on him when she lies about where she's going, so he follows her and...
-->''"Tonight I kinda get the feeling/My girl is up to something, Something that is no good/ She said she only had a meeting/ But she is dressed for something, Something that is no good/ [[YourCheatingHeart Now I'm not saying that she's cheating,]] But seeing is believing/ [[InVinoVeritas Can't believe it, What I'm seeing when I stepped inside.]]"''

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[[folder:Video Games]]
* ''VideoGame/LeisureSuitLarry 7'' got this one, cranked up to 20, with HotLibrarian [[PunnyName Victorian Principles]].
* Nekoko from ''Yume Miru Kusuri'' [[spoiler:though this is more of drug effect]].
* ''VideoGame/YouDontKnowJack'' Movies parodied this one for one of the Question 18 segues:
--> Question 18: Honor student by day... ''stripper by night!''
* Possibly Litchi from ''VideoGame/BlazBlue''. Despite her incredibly skimpy battle clothes, her personality is fairly conservative. However, supplement materials and a couple of gag endings say that when she gets drunk she gets rather...insistent.
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[[folder:Western Animation]]
* In ''{{Futurama}}'', a prim bureaucrat is utterly turned on after hours by Fry's horrifyingly slobby lifestyle.
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