Conveniently-Common Kink

"The Web brings people together because no matter what kind of a twisted sexual mutant you happen to be, you've got millions of pals out there. Type in 'Find people that have sex with goats that are on fire' and the computer will say, 'Specify type of goat.' "

- Rich Jeni

Alice and Bob has a problem. She's recently realized that she gets really, really excited from waxing cucumbers. But who on Earth would share a fetish for applying a shiny glaze to vegetables? Surely Alice will have to keep this desire a deep, dark secret.

Surprise! It's been Bob's life-long ambition to become a full-time cucumber waxer, he just never found anyone he could share it with. And Alice and Bob live in total gratification ever after, or at least for the duration of the story.

A staple of erotic fiction: love is never having to explain your fantasies, whoever you choose for a partner will happen to share them (or at least be really receptive), regardless of how unlikely this is or in what situation you present them. Some stories make angsting over this a plot point; most don't try.

A form of Contrived Coincidence. May be a symptom of Author Appeal. Compare Everyone Is Bi, Rule 34.

Fan Fiction

 * Strangely, a freakishly large amount of Buffy the Vampire Slayer Lemon/Smut fics are BDSM or bondage or something along the lines of that. And everyone involved, whether Joyce, Willow or anyone else is into it - though, to be fair, no Buffy character ever passed up an opportunity to comment on the kinky potential of chains, Joyce included, so there's at least some evidence here. Less justifiable are Crack Ship options such as Buffy/Dawn getting the same treatment.
 * There is one story where the kinks were shared by an entire, apparently bisexual, household of newly activated Slayers, Willow, Dawn, Buffy, Xander, Faith and the neighbors, who, when it comes to the female ones, including an underage girl, were also apparently all bi. Everyone Is Bi to a new level. The kinks: Humiliation, spanking, BDSM, public nudity, lesbian incest between sisters and groping.
 * A subtrope of this would be "Hooray, You're Gay!": in fanfiction, if one character is gay and in love (or lust) with another, then (with a few angsty exceptions) that other character WILL be gay and in mutual love/lust, no matter how unlikely.
 * How unlikely? It can go to "Hooray, You're Gay and in love with your sister who is in love with you!"
 * Weight gain and inflation fetish stories will commonly have the main girl(s) happen to find at least one person who's into whatever fetish they're subjected to. In cases of Fan Fiction, the girl's love interest will suddenly have an interest in this fetish for plot convenience.

Film

 * Fat Slags goes a step further. While the titular characters are in London, they don't just happen to meet a Chubby Chaser. Instead, a mega-rich media mogul gets hit in the head, suffers a change of personality and "coincidentally" becomes a Chubby Chaser.
 * Subverted in Pennies From Heaven, where the wife finally goes along with the main character's fetish (lipsticked nipples) in such a way that it practically plays as a rape scene. The incident signifies the extreme dysfunction of the marriage, and is a contributing cause of all kinds of ugly consequences.
 * Parodied in Not Another Teen Movie, when Catherine laments that she's never had a guy take a dump on her chest. A teenaged boy proclaims, "That's appalling! I can't believe no one's ever taken a dump on your chest."
 * In Secretary, Maggie Gyllenhaal wants to be a submissive. She works for James Spader . Coitus Ensues.

Literature

 * Surprisingly happens to (of all people, really) ultimate Badass Victor Cachat. After he got himself a girlfriend at last, after all those years of being a Celibate Hero, he kinda snaps and heaps all his pent-up frustration (they've also got a serious argument just before) on her when they finally found the time to do the horizontal mambo, and wallows in misery and self-guilt afterwards. To his astonishment, Thandi just so happened to be into SM, and actually wanted it more. Hilarity Ensued indeed -- the teasing poor Victor received from her and his self-appointed Cool Big Sis Ginny Usher made him "dark and utterly miserable".
 * In addition to poor Victor, there was the collision resulting from the meeting of Thandi's Amazon Brigade of genetically-engineered mercenaries/terrorists with the genetically-engineered former slaves/terrorists/freedom fighters of Jeremy X. Two groups of hardened killers finding their (metaphorical) Opposite Sex Clone, and stuff happens.
 * The YA novel Flipside provides a non-pornographic example. The main thrust of the story, so to speak, is the coming of age of a Wholesome Crossdresser, and it just so happens that the girl he's been lusting after for years becomes attracted to him when he's in a dress.
 * There's a book called the Best Case Scenario Handbook (a parody of the Worst Case Scenario one) that includes an example of these among various examples of extreme cases of good fortune. It's to the effect of someone's wife or girlfriend confessing to an interest in an unidentified sexual act that happened to be that guy's hidden fetish.

Live Action TV
"Sally: I cant believe I'm dating a man with a pregnancy fetish!
 * Subverted in Sex and the City, where the protagonist wrestles with herself over whether to indulge her date's urination fetish. She offers him compromises ("we could use warm tea..."), but is rebuffed.
 * Played straight when Miranda's boyfriend likes to talk dirty during sex. At first she is reluctant to do so, as he urges her to talk dirty. Then she starts to like it.
 * A subversion from an Scrubs: Elliot finally breaks down her boyfriend's resistance, and gets him to tell her (off-screen) what his sexual fantasy is. She instantly flees in horrified disgust. All the audience learns is that it doesn't involve chains, whips, candle wax, role-playing, lasers, hamsters, or Mexican apple thieves.
 * Wasn't it just that he wanted to have sex on top of the sheets, instead of under them?
 * With the lights on!
 * This from Coupling;

Patrick: I can't believe I'm dating a woman who suddenly wants a baby!

Sally: How is this ever going to work?"

Stand Up Comedy

 * Steven Wright once recounted a tale in which he boarded a bus and met a nymphomaniac who's into Jewish cowboys. After she explained her problem to him, Steven introduced himself as "Bucky Goldstein".
 * Lewis Grizzard also told a variation of it occurring on a train, and the fellow introducing himself to the nympho with the line, "Hopalong Ginsberg, at your service".
 * Louis CK once told a joke about going out with a girl who had a rape fetish, they made out but never had sex because she stopped his advances. Later, when she asked him why they didn't have sex he said "because I thought you didn't want to." She then told him she enjoys when a guy "just holds me down and fucks me!" Played straight when Louie informs her "oh, you should have told me, I would have happily done that for you." Then subverted when the girl tells him it has to be forced to feel real and dangerous, to which he responds "I'm not gunna rape you on the off chance that you're into that shit!"

Web Original

 * "My miniature stallion". For people who don't want to actually see it, it's 2 people discussing on camera how they found true love and got married over their shared love of.
 * The furry propensity towards these was deconstructed in these three stories. In each story, a character gets their hands on a latex transformative goo that just happens to be their fetish. Respectively,

Web Comics

 * Saturday Morning Breakfast Cereal plays with this.
 * Collar 6 - The entire city is apparently into BDSM.
 * Make that the world. Recent strips show that the divergent history of this world was an ancient (as in, Roman or earlier) discovery of Atlantis, and how they had perfected a lifestyle/society/government that combined BDSM with spirituality in such a way that it lead to world peace and sexual-lifestyle-based Ki Attacks. Yes, seriously. The few areas of the world that didn't ascribe to this are referred to as "Puritan."
 * In El Goonish Shive, Elliot and Sarah both have superhero related fantasies.
 * Or for the obvious pairing, Tedd, who's into Gender Bending and furries, and Grace, who is a shapeshifting alien chimera squirrel-girl and deeply in love with Tedd.
 * The Basitins in Two Kinds have a Word of God-supported species-wide foot fetish. Considering how sexually-repressed they are, nudity can stop a room full of Eastern Basitins with ease.
 * In spite of clothes being a cultural option in Bittersweet Candy Bowl, if you wear clothes and show your undergarments, things can get interesting.

Western Animation
"Asian Reporter Tricia Takanawa: Tom, I'm standing in the bedroom of Judy and Glen Isaacs. 10 years married and still in love. What's their secret? Judy has an inoperable brain tumor the size of my fist, and that just happens to be Glen's fetish."
 * Family Guy: