In End of Evangelion, Maya is revealed to be a lesbian with an unrequited crush on her "sempai", Ritsuko, who is very much into manly men. This also caused Kaji's earlier attempts to flirt with her to fail.
Falco Lombardi and Katt Monroe in the canonical Star Fox manga Farewell, Beloved Falco. The Incompatible Orientation is that Falco has never wanted a girlfriend, nor will he ever want one. It becomes blatantly clear that Falco has never felt swayed or had any sort of Male Gaze for any female character. Though whether this makes him gay or asexual is never made clear from only this context. The other contexts, however...
Likewise, Kitagawa definitely has a thing for her teacher Mika, who doesn't appear to swing that way at all.
Toyed around with endlessly in Maria†Holic. The main character goes to an all-female school to meet girls, and basically falls in love with every girl she meets. However it seems like really no one she has met is a lesbian.
Saber Marionette J makes a running gag of the attraction the flamingly gay rich boy Hanigata has for the poor, industrious (and fundamentally straight) Otaru.
In WORKING!!, Jun is having a hard time with his feelings for his colleague Yachiyo, who in turn is in love with Kyouko, her female boss at the family restaurant they work at.
Questionable - although Yachiyo is utterly devoted to Kyouko and would almost certainly be willing. There is no direct evidence that they have ever been lovers or that either have ever had lesbian sex with anyone.
Kou from Aoi Hana has it tough, since Kyouko, the girl he is engaged to, is lesbian—at least judging by her crush on Yasuko.
Mahou Tsukai Tai! takes the cake for having multiple cases in the same Love Dodecahedron. Aburatsubo, the bishonen gay vice-president is crushing on Takeo, the straight club president (who lusts for Cute Witch Sae, who is too shy to express her feelings for Takeo). Meanwhile Nanaka (another Cute Witch and club member) has a crush on Aburatsubo, which he can't return either. They have a heartwarming moment when she confesses and he turns her down... but admits that he knows fully well how she feels, unable to have the one you love.
Vampire Game: Laphiji is in love with Seiliez, his Not Blood Sibling. Unfortunately for him Seiliez is shown to be straight considering his crush on Ishtar. However this can also be subverted for it is hinted later on that Laphiji and Seiliez do begin a sexual relationship... albeit one that is likely to not last long.
Sara from Tenshi Ni Narumon develops a big crush on Mikael in the second season but it never goes anywhere because first, Mikael has only eyes for anything related to angels and second, he's already in love with his male teacher, Raphael - even if he has problems admitting the fact to himself
Similarly, Natsumi has some questionable feelings towards her deceased older brother Fuyuki over whom she obsesses throughout the whole series, but again, it never goes anywhere because first, Fuyuki is well, dead and he turned into an angel Raphael and second he's in love with his male student, Mikael
In Hayate the Combat Butler, Luca confesses to Hayate that if he were a guy, she'd have fallen for him. She thinks he's a girl because she's only met him while he was crossdressed, so she doesn't know that Hayate is actually a guy, and that she actually did confess to him because of it.
Even before the confession he didn't want to let her know he's actually a guy.
Both Miki and Ayumu have expressed romantic interest in Hinagiku as well, and decided to take a backseat to things, since Hinagiku is smitten with male Hayate. Ayumu has expressed interest in Hayate as well, allowing her to possibly supercede the limits of this trope without changing any orientations.
Bakemonogatari: Suruga is in love with Hitagi who is straight and dating Koyomi.
Makoto from Wandering Son has fallen for several boys (and men), however right now the object of his affections is his (ignorant and immature) straight friend.
In Shinshi Doumei Cross, student council president Shizumasa aka Takanari has so many women chasing after him that he has Maguri, another male member of the Student Council, pretend to be his lover. The problem with this arrangement? Maguri actually does have feelings for him, and has to sit by and watch while he chases the main heroine instead.
Camp GayArms Dealer Fred Luo is in love with straight Handsome Lech Gene Starwind from Outlaw Star, but neither of them seems to Gayngst about it. Gene uses Fred's crush to score better deals on parts and weapons, and Fred uses Gene's desperation for said parts as a bargaining chip in his less...legitimate business endeavors.
Lampshaded when Fred tells Gene that, in exchange for supplies, he 'owes him a favor'. Gene doesn't miss a beat before responding "I'm not going to sleep with you Fred."
Furui of Poor Poor Lips, despite his initial dislike towards her, ends up having a crush on Ren. This causes him no small amount of angst since one of the causes for his initial dislike is his discomfort around the fact that Ren is an out of the closet lesbian.
Ladies' man Sanji of One Piece is wanted by the entire population of the gay island Kamabakka Kingdom.
Sekirei has it's own way with this trope. Homura has an unstable gender, but mentally identifies himself as male. At the start of the story he was physically male, and had been trying to find an Ashikabi who was female. However, as time went on his body began reacting to main character Minato, who is a heterosexual male. As a result, Homura began tuning into a woman. It's not clear if the transformation was complete by the time he was finally "winged", but the character now has breasts as well as more feminine features, and is pretty annoyed and uncomfortable with the whole situation. Poor, guy/girl.
An example of Incompatible EVERYTHING with Cuuko (Cthuguha). She's got a lesbian crush on Nyarko, who is both straight and head-over-heels in love with Mahiro Yasaka. On top of that, Nyarlathotepians and Cthuguhans are mortal enemies, so their very natures are in conflict, and the idea of two even being friends is unheard of; Nyarko tells Mahiro that Cuuko's family would be utterly shamed if news of the crush got out. Of course, Cuuko's also kinda inconsistent on this; one arc has Mahiro and Nyarko swap bodies, and Cuuko immediately puts the moves on Mahiro-in-Nyarko, saying "Just Nyarko's body is fine."
Of course, part of the story's whole hook is this. Mahiro is attracted to Nyarko as a person, but is put off by the knowledge that she's Nyarlathotep, the malign god of chaos and madness from the Cthulhu Mythos. The fact that she could shatter his sanity just by changing forms, and that she might be lying about being in love with him just to screw with him, are deal-breakers in Mahiro's eyes, but over time he grows to accept her honesty and his true feelings for her.
Hasta is also in love with Mahiro, and he's both a Humanoid Abomination (Hastur) and a guy. Ironically, he's the least likely of the trio to get on Mahiro's nerves.
Renee Montoya, by that time the new Question, was involved in another example, this time on the other side. Both in Birds of Prey and in the Question back-up feature in Detective Comics, Question teamed up repeatedly with Huntress, and it became quite clear that she was interested in Huntress (Helena Bertinelli) romantically. The storyline never had time to develop very far before DC's "New 52" reboot, but Huntress had always been portrayed as straight, and was not even aware that Question was gay, at one point asking if she and the previous Question, Vic Sage, had been lovers.
Lipstick Lesbian Karolina spent much of the first two volumes of Runaways pining for her best friend, Nico, who was a little shocked when K finally tried to kiss her. After beginning a relationship with shapeshifting Skrull Xavin, who takes on the form of a human girl, Karolina loses romantic interest in Nico. Then again, this hasn't stopped them having Ship Tease moments since.
Northstar once had a crush on Iceman. It didn't take him long to realize it would never happen, since in his own words "He's straight. End of story." (It was only introduced to squash fan speculation that Iceman might be gay.)
Subverted in Exiles: Morph had a crush on teammate Sunfire without realizing she was a lesbian. When she made The Reveal, he accepted it wholeheartedly and continued to act as a brother figure to her, even supporting her relationship with Spider-Woman. (Well, accepted it wholeheartedly after giving the "Hey, I'm a shapeshifter, I can do lesbian" line a shot...)
In Buffy the Vampire Slayer Season 8 comics female Slayer Satsu falls in love with Buffy and they have sex at least twice. But Kennedy, another lesbian Slayer, dissuades Satsu from pursuing a relationship with her. Why? Because she claims that ultimately, Buffy is straight.
Tom Pearce never stood a chnce with the object of his crush in Camelot 3000. Of course, it was further complicated by the Gender Bender nature of reincarnation.
At one point in Superman comics, Dan Turpin of the Metropolis Special Crimes Unit had a crush on his boss, Maggie Sawyer, even going as far as to propose to her. She explained the situation to him (off-panel).
In Respawn Of The Dead, the RED Spy is in love with the RED Engineer, who is both straight, and has a family back home. Needless to say the Engineer rejects him (not helped along by the many atrocious acts that Spy commits over the course of the story), and the Spy ends up killing himself.
In Fallout: Equestria Lilpip grows up with a crush on Velvet Remedy, who is straight. They later become best friends and Velvet goes so far as to become something of a motherly figure to her. Notable in that it's Lilpip's feelings for Velvet that compel her to leave the Stable when Velvet runs away. So this trope actually sets off the plot! (Not that kind, get your mind out of the gutter!)
The Conversion Bureau Not Alone has Andrew (a male human) and Ice Breaker (a male pony). Andrew admits that he's developed a crush on Ice Breaker (well aware of the incredible likelihood of this trope being in force). It is, and they remain Just Friends.
Dragon Ball Abridged's Dende, who comes from an race with No Biological Sex, finds himself smitten by Bulma's breasts. Later, we find he has something of a crush on Gohan, as the two had been friends for a while. After a few months of living together, he confesses his love, to Gohan's confusion. Poor guy...
In You Got HaruhiRolled!, Kyouko has a MAJOR lesbian crush on Sasaki, who will have none of it. The only person Sasaki feels attraction towards is herself. Kyouko is completely oblivious to this.
In This Nearly Was Mine, Frederic Horshoepin has a massive crush on his bandmate Octavia. Unfortunately for him, this universe has the VinylTavia ship in full play, so he's stuck watching the love of his life making out with the DJ mare.
Reading Rainbowverse has Big Mac's crush on Twilight, who admits she doesn't see stallions that way.
In The Dashverse, Cloud Kicker eventually confesses to Twilight that she actually is in love with Rainbow Dash. Unfortunately for her, Dash is not only straight, but completely oblivious to her feelings, as she just assumes its part of Cloud Kicker's usual personality.
Some fans of the Picard/Q pairing from Star Trek have pointed out the implausibility of a stout heterosexual man like Captain Picard — who has had several female love interests in the show — changing his preferences by pursuing a relationship with Q's male form. As an Energy Being Q has no natural mortal form, and could just as easily have been a female as a male, and Q points this out to Picard in the show's canon. So as a way around this incompatibility some fanfic writers have used the premise of Q changing into a female form to pursue a relationship with Picard, citing how an energy being wouldn't really have an attachment to any particular mortal form and that none of it matters so long as he can pursue his love interest.
Gus Van Sant's 1991 film "My Own Private Idaho" provides a great example of this trope. Mike Waters (played by River Phoenix) is in love with his straight best friend, Scott Favor (played by Keanu Reeves). It doesn't end well.
The Kevin Smith film Chasing Amy is primarily about a straight man trying to win the affections of a lesbian woman he fell in love with. And for the record, her name isn't Amy. The title regards a story within the story.
To make matters more complicated the woman in question is technically bisexual but identifies lesbian, and this confuses everybody.
Not to mention the possibility that the straight guy's best friend may be feeling some secret Ho Yay for him as well....thus leading to the disastrous suggestion Holden makes at the end of the movie.
In Threesome: Alex is in love with Eddy, but he's gay and in love with Stuart - who is straight and in love with Alex.
The Object of My Affection is all about this trope; a woman falls for the gay man who becomes her roommate after her husband leaves her.
In Election, this is why Lisa stops being friends with Tammy. She was straight (and only "experimenting"), while Tammy was a lesbian who thought that the two of them were in love.
At the end of The Childrens Hour it's revealed that Martha was in love with Karen, her straight best friend who was going to get married, the entire time they've known each other.
Occurs in the film The Upside Of Anger, when the youngest daughter Lavender tries to seduce a classmate and he rebuffs her by declaring he's gay.
Lavender: Have you ever had gay sex? What about sex with a woman? Just have sex with me and if you don't like it, then you can be gay.
Gorden: That's really nice of you. (leaves the room)
In Radio Days, Bea is desperate to get married and goes on a string of dates looking for love. When she tells her date Fred that she has a crush on him, he comes out to her. Being the 1940s, it takes Bea a few minutes to fully understand what he means.
Prudence in Across the Universe falls for both the cheerleader chick and Sadie during the course of the film. Both are straight, and seeing someone else. The unrequited nature of her love for Sadie causes her to suffer a Heroic BSOD until her friends sing to her about how beautiful she is and help (literally) coax her out of the closet.
Sort of the premise of a few necrophilia-themed films, like Kissed and Nekromantik 2. The former even ends with the man who is in love with the main character killing himself so he can truly be with her.
In Gone, Dekka has a crush on Brianna, who is straight.
In Doctrine of Labyrinths, especially at the beginning of the second book, Felix (gay man) is attracted to Mildmay (straight man). Incompatible Orientation isn't even the biggest problem here; the biggest problem is that they're brothers. Less squickily, a girl they meet on a journey develops a crush on Felix and decides it's true love; he has to explain to her that no, he's not interested.
The Inda series by Sherwood Smith combines this with All Love Is Unrequited. Hadand (straight woman) is in love with Evred (gay man), who's in love with Inda (straight man). To make things more complicated, Evred and Hadand are in a highly political Arranged Marriage (they're king and queen; he's an Unexpected Successor and she was betrothed to the previous heir), Inda and Hadand are siblings, and Inda is Evred's military second-in-command.
The Rules of Attraction features a bisexual college student in love with another guy, but this guy's straight and in love with the former's (female) best friend.
In Master and Commander, Mr. Marshall, a known "paederast," is hopelessly attracted to Captain Aubrey.
Lord John's hopelessly unrequited love for Jamie in the Outlander series.
In The Princess Series near the end of the first book Snow White is placed back in her magic coma and can only be awaken by a True Love's Kiss. Talia (Sleeping Beauty) kisses and awakes her openly showing her love for Snow White for the first time. Snow is a major flirt who is blind to Talia's true feelings. Talia seems to realize it wouldn't work out so tells Snow that she just used a spell to wake Snow.
In Kiss by Jacqueline Wilson, shy Sylvie believes she is in love with her best friend Carl, and is convinced they will one day get married. However, Carl discovers he's actually gay, and Sylvie not only has to deal with the aftermath (including his being bullied and attempting suicide) but also come to accept that he can never love her as more than a friend.
In the Girls series, Ellie has a very strong crush on an older guy she meets in town, and pretends to her friends that he is her boyfriend Dan (causing her embarrassment when they meet the real Dan, who is awkward and nerdy.) It turns out that the older guy is gay, but he and Ellie become good friends later on.
Luna by Julie Anne Peters includes a subplot about a straight girl being love with another straight girl ... because the girl she likes was born with a male body and hasn't told her friend she's transsexual yet. The friend with a crush thinks 'he' is gay - "But gay people get married, right? They have kids. He could change." There is some tension after The Reveal, but they stay friends.
In Thief of Souls, Drew (who is gay) has a crush on Michael (who is straight).
Arianne Martell also attempted to seduce Renly when the Baratheons visited Sunspear, but Renly seemed mostly amused by her attempts.
Jon Connington was in love with Rhaegar Targaryen, who was straight.
Comes into play in Robin Hobb's Farseer and particularly Tawny Man trilogies between hero Fitz, who is quite straight, and his best friend the Fool, who is quite in love with Fitz. The Fool is quite open about his feelings, though he denies that there's anything sexual implicit in love; the situation serves, however, as a major source of discomfort for Fitz once rumors start flying about their relationship. Possible subversion in that the Fool might be a Wholesome Crossdresser, but probably not.
In the Heralds of Valdemar series, Melenna feels this way about Vanyel in the Last Herald-Mage trilogy.
In the Alex Delaware novel Self Defense, one of Alex's patients, Lucy, tells him that she's falling for Alex's Friend on the Force Milo. This puts Alex in a very awkward position, since he can't violate Milo's privacy by telling Lucy that Milo is gay, and can't violate Lucy's by telling Milo about the crush.
In Sputnik Sweetheart, K (the narrator, straight man) is in love with Sumire his best friend. She in turn meets and falls in love with Miu, another woman.
The Heroes of Olympus: In The House of Hades, it's revealed that Nico di Angelo has/had a crush on Percy Jackson. Percy, who fell into the depths of Tartarus to be with Annabeth.
Live Action TV
Season 4 of Heroes has Claire's roomate Gretchen reveal herself as a bisexual who has a crush on her. This appears to be a case of incompatible Orientation as Claire is thought to be completely straight at this point. This however is subverted in the episode "Pass/Fail" when Claire officially declares she also has feelings for Gretchen.
Kurt also starts making out with and dating Brittany in one episode because he feared that his father saw the heterosexual Finn as a better son. His dad is understandably confused.
Depressingly, this also happens between Sam and Kurt. Kurt was only vaguely interested in him and more just determined to make him admit he dyes his hair. (Which he does.) This pairing seems to be 10% canon, 90% indignant fandom who are mad that Ryan Murphychanged his mind at the last minute (again) about Sam being Kurt's love interest.
Also, Blaine and Rachel, if only for one episode. After a drunk kiss with Rachel, Blaine (who has until then believed himself to be gay) decides that maybe he's actually bisexual. They go on a date, but when they kiss again while sober, Blaine realises that he was wrong about being bisexual. Subverted, as Rachel didn't seem to actually be in love with Blaine. It seems that the fact that he can sing and is a good kisser is enough for her to decide to date him, and she's positively thrilled when he tells her that he's gay after all:
Rachel: That was amazing! I am speechless! I just had a relationship with a guy that turned out to be gay; that is song writing gold!
Also, in one episode, after Kurt gives Rachel a pep-talk, she says that she wishes he was her boyfriend. It's mostly joking though, since they are both taken.
Blaine also gets two of the girls from Dalton's sister school charmed by his performance of Animal and try to give him their phone numbers, asking him to call them. His response? "Sweet, but not your team."
Santana ultimately turns out to be this for Puck. He takes it well, though; by the time she's on the road to coming out, he's moved on, and in the episode where the club helps Santana dealing with her outing, he says that he knows that he "was just a phase" and is fine with it.
As if "Sadie Hawkins", Tina believes Blaine (gay) is her soulmate despite him turning her down for obvious reasons. Blaine has a massive crush on Sam (straight) but won't act on it because he doesn't want to be a "predatory gay" and because he's "proud that a gay guy can be friend with a straight guy."
In the second season, Maxxie, who is gay, is stalked by a girl whom everyone calls Sketch. She sabotages her way into the school musical just so that she can kiss him, convinced she can make him love her. She also follows him home, sneaks into his house, masturbates on his bed and then hides under it while he is sleeping. Now you know how she got that name. The strangest thing about Sketch is that she is aware that Maxxie's gay and somehow thinks that by dressing in masculine clothes and binding her breasts, she'll break through the Incompatible Orientation barrier. When she decides to go after his best mate Anwar (who is straight) instead, she stops binding and starts wearing more frills and make-up.
Naomi tries to tell Emily this in the third season, but it's eventually revealed that she was just Armoured Closet Gay and has always loved Emily and only Emily.
Naomi: Me, not muff-muncher. Me, cock-cruncher.
J.J and Emily. Emily offered to take his virginity the same day that she came out of the closet.
Emily: This is a one-time only charity event, you understand?
J.J.: Got you. Because you are gay.
Emily: Yes, I'm gay. Get on with it.
This understanding didn't stop him from hoping for the possibility of a relationship when she asked him to the Love Ball, but it turned out that he was her beard, and she left him when Naomi showed up.
Cook and Naomi. She tried to jump him when she was still in denial about her sexuality, but stopped after about forty seconds of mad snogging, since she realized that she didn't want to do it. In the fourth season they share a big heart-to-heart, and Naomi ends up giving him a very platonic kiss, giving us:
Cook: [beat] for f—ks sake, I’m never gonna get to bone you, am I?
Naomi: [Very matter of factly] No, I love someone.
When new character Alex is introduced in the sixth season, Liv gets a crush on him, only for him to reveal that he's gay when she admits her feelings.
The American remake has a very strange version of this with lesbian Tea and straight Tony. Tea sleeps with Tony as a joke, but he gets feelings for her. Yet, for some reason, she keeps sleeping with him, out of either a power trip or because she's confusing their platonic chemistry with sexual chemistry, depending on which interview you read. It ended up as a Relationship Writing Fumble since Tony and Tea were more believable together than Tea with her actual girlfriend and love interest, Betty. And yet, the show kept insisting that she was a complete, 100% lesbian with no interest in Tony.
In a Will and Grace episode, Grace encounters a Fag Hag who is in love with her gay best friend. Having been down this road, Grace tells her that she has absolutely no shot with him whatsoever. She denies it at first before confessing why they can't be together despite their perfect compatibility.
For that matter, virtually the entire premise for the series ("I wanted to raise the kids to be Jewish; you wanted to sleep with men").
My So-Called Life: After her disastrous crush on Brian, Delia has that glorious dance scene with Rickie. By the last episode, the only one oblivious to her newfound crush is Rickie. When he tries to reciprocate, she tells him she knows he's gay (in that awkward, teenage way—"You're gay, right?")
In 'Allo 'Allo!, the very campy Gruber is hopelessly infatuated with the very straight Rene, who is frequently discomforted by the fact that Gruber "fancies" him. (Ironically, Gorden Kaye, the actor who played Rene, is in real life a very content and "out" gay man.) The series finale showed that Gruber had married Helga after the war and had many children with her, perhaps making this a further case of Incompatible Orientation from her side.
Played for comedy in an episode of The Catherine Tate Show where a lesbian nurse falls in love with (the very man-eating) Bernie.
In a second season episode of the television comedy Frasier, "The Matchmaker", Frasier introduces Daphne to his new boss, Tom Duran (not realizing that Tom is, in fact, gay). Daphne finds herself immediately smitten to Duran, only to be crushed anew when she learns that he could never share her attraction.
In a sub-plot, Tom finds himself attracted to the heterosexual Frasier. At one point he even confesses to Frasier that he had no idea the man was straight.
In Waterloo Road, Phil and Roz find that they're compatible personality wise, and form a relationship which runs smoothly until Roz falls in love with her female teacher. At the climax of this plot point, Phil and Roz agree that since Roz is now a lesbian, they probably wouldn't go well together after all.
In The George Lopez Show, this is subverted in the episode "What George Doesn't Noah". Carmen brings home what seems to be the ideal boyfriend, Noah, after dating bad boy Zack. George and Benny spy on Noah and find him with another man in a movie theater. Turns out, Carmen was using Noah as a cover so that she could date Zack secretly.
In Lip Service, Ed has a hopelessly unrequited crush on his lesbian friend Tess.
Buffy: Willow, you're a gay woman! And he...isn't!
Willow: This isn't about his physical presence! It's about his heart.
Anya: His physical presence has a penis!
Willow: I can work around it!
Willow's case overall in the series tends to fall under No Bisexuals: now that we've established her as lesbian, we just couldn't have her be interested in a man, despite her previous physical relationships with Oz and Xander.
In the same episode Willow attempts to get around this trope by using a spell to change the man into a woman. Fortunately for him Xander and Spike stop her from completing the spell.
Buffy is this with Satsu. Even though Buffy is flattered, and sleeps with her (twice!), she is quite adamant that she is not a lesbian and they can't be together.
Fiona from Degrassi has come out of the closet, in the process revealing she had a thing for her best friend Holly J. However, after Holly J finds out, she tries to set Fiona up with another girl at a school dance. This doesn't amuse Fiona, but the two later reconcile, remaining best friends.
In another episode, Fiona's locker is near the hockey team's lockers, and Dallas hits on her. She then says that she and her girlfriend Imogen are lesbians, but he doesn't believe her, since they don't kiss.
In The Nanny episode "The Playwright", Maggie is in love with Gracie's ballet teacher, who helped her with her make-up and does great Liza Minelli impressions. Fran is just suspicious until Maggie says something about him getting along well with his "roommate" Chuck.
The short-lived John Ritter show Hooperman featured a Running Gag involving a gay cop named Rick and a fellow officer named Mo who repeatedly hit on him despite him having no interest in women.
Sherlock: There's a lot of this as the titular character is basically asexual and aromantic, making him incompatible with everyone. (Heterosexual) Molly Hooper's unrequited crush pales in comparison to the hideously confusing love triangle between Sherlock, John, and Irene. Sherlock is asexual, John constantly reminds everyone that he is heterosexual, and Irene is a lesbian. Yet Irene becomes sexually fascinated with Sherlock and observes that John is in romantic love with Sherlock whether he realizes it or not (with a physical dimension - John knocks Sherlock around to fake an alibi but can't bring himself to hit Sherlock's nose or teeth to make it convincing). Sherlock has a tongue-tied sexual fixation on Irene, while also feeling romantic love with no apparent physical dimension towards John. In short: the lesbian is in love with a man, the heterosexual man is in love with the same man, and the asexual is in love with both of them.
Doctor Who: In "Rose," the Ninth Doctor flips through one of Jackie Tyler's gossip mags and exclaims, "Oh, that'll never work! He's gay and she's an alien!"
Rachel reveals that she kissed one of her sorority sisters, which Phoebe doesn't believe. Rachel takes Phoebe to dinner with the sorority sister, who insists she has no idea what Rachel is talking about. After dinner, the sorority sister reveals that after that kiss, she started feeling differently about Rachel and in fact pictures her face when she makes love to her husband. Rachel obviously does not return the feelings.
Joey: It's like my favorite bedtime story come true: 'The Princess, the Stable Boy, and the Lesbian!'
Ross is divorced from his lesbian ex wife Carol but still retains feelings for her early on the show and even in later seasons he seems to be sure they could have been happy together had it not been for Carol's sexuality.
The reality show Boy Meets Boy had a gay male bachelor choose a mate among several guys, but unknown to him, half the guys were straight and planted by the show to see if he'd fall for one. One of the straight guys, however, had a change of heart when he grew to like the bachelor as a person. He eliminated himself because he wanted him to have a real chance to find love.
An episode of The Thin Blue Line concerns Constable Maggie Habib meeting a handsome firefighter and trying everything to get into bed with him. In the end of the episode, it's revealed that he hasn't touched her because his interests were focused on her colleague, Constable Kevin Goody, who's spent the whole series pining after her. In the last scene they all sit at a pub musing about their love triangle woes.
In Once Upon a TimeMulan finally gets the guts to tell Aurora she's in love with her...and Aurora beats her to the punch by announcing she's pregnant.
On Happy Endings, Max's old high school girlfriend is visiting and she and Dave hit it off. Max gets very upset by this, which Dave can't understand since Max is gay and obviously won't be getting back together with her. Max, in order to make Dave jealous, grabs Alex (Dave's ex-fiance) and kisses her, but Dave doesn't care because he knows it doesn't mean anything. Then Alex, who enjoyed the kiss, spends the rest of the episode mooning after Max (while Penny tries in vain to get her to see it's hopeless).
The Tatu song Malchik Gay (or Mal'chik Gey, "Gay Boy" in Russian) is about a girl in love with a gay boy who spurns her.
Amore Si by Tanita Tikaram is a heartfelt evocation of unrequited homosexual attraction where the singers' acceptance of the impossibility of a relationship collides with blind love. Going on with a friends-only relationship is tearing the protagonist apart.
White Town's "Your Woman" (later covered by Tyler James), about a straight guy in love with a gay woman, which makes the line "I could never be your woman" kinda obvious.
A different interpretation has the song be about a gay man in love with a straight man, which is still this trope.
"She'll Never Be Your Man" by Chris Cornell, which is either about the bitterness and resentment of either a straight man losing his girlfriend to a gay woman, or a gay man losing his boyfriend to a straight woman.
"Ziggy", from the famous (in France) musical Starmania (known as Tycoon outside of France), a song later covered by Céline Dion, is about a barmaid (who somehow serves as narrator of the musical) who is in love with a very gay fan of David Bowie.
Inspired by something that actually happened to Rivers Cuomo, but ironically in reality it turned out to be a case of Mistaken for Gay: He wrote the song after harboring a crush on a girl, then noticing a pink triangle patch on her backpack one day (not "on her sleeve" as the lyrics state). However, long after he'd already written the song and fallen out of contact with the girl in question, he learned that she was straight, and was wearing the symbol to show her support of gay rights.
Reel Big Fish's "She Has a Girlfriend Now" is about a guy despairing that his ex now only dates women. He offers to get a sex change to appease her, causing the girl to croon "Oh, that's so sweet!"
At the end of the music video to "Call Me Maybe" by Carly Rae Jepsen, it turns out that the dude she's been obsessing over is gay. This is followed by Carly giving an expression of pure, undiluted "WTF".
And the guy is interested in the guitarist in Carly's band. It's implied that this too is a case of Incompatible Orientation.
This is one interpretation of R.E.M.'s song "Losing My Religion": that it's about the (male) singer's gay crush on a straight man.
The Pet Shop Boys' cover of Oh Romeo's "Try It (I'm in Love with A Married Man)" changes the perspective from that of a woman in an adulterous relationship to a gay man in love with a married straight man.
"Beautifully," by Jay Brannan is about a girl very much in love with a boy who can't return her feelings.
An interpretation of Fall Out Boy's "Sugar We're Goin Down" suggests this: the lyrics in the liner notes say "wishing to be the friction in his jeans" instead of the recorded version's "in your jeans". The song also includes references to "watching [a couple making love] from the closet" and "sleeping for the wrong team."
This happens tragically in the Twist Ending to the music video for K.will's song "Please Don't..." Spoiler alert: Seo In Guk's character is in love with his best friend, not his best friend's girl.
Joanie Caucus from Doonesbury had a crush on Andy Lippincott, who turned out to be gay. She was with him when he died of AIDS. Earlier in their relationship she thinks he's married, but he reveals that's not the problem.
Andy: Joanie, I'm gay. Joanie: There's nothing wrong with that. I'm pretty cheerful myself most of the time. Andy: No, I mean... Joanie: Oh my God.
Implied to be the reason Juhani and Dak Vessar had a falling out in Knights of the Old Republic. They were both Jedi Padawans, but started to have their doubts about the Order. Dak made up his mind to run away, and tried to take Juhani with him, pleading he loved her. Unfortunately, Dak...wasn'tJuhani'stype.
The male player character can try to flirt with Juhani. It doesn't work very well; she's openly disgusted in fact.
A number of Female Shepard players probably ran into this regarding Subject Zero. If you keep talking to her after her personal mission, she'll assume you're interested and "let you down" surprisingly gently, considering what she's normally like.
Likewise with Mordin (from an Asexual species) and Shepard in the same game. If Shepard keeps going back and talking to Mordin often enough and is not otherwise in a relationship, Mordin will assume that Shepard is expressing "interest" in him, and lets him/her down gently. Shepard then has the option of saying that his stopping by for conversation so frequently is Not What It Looks Like. Or you can run with it and sarcastically thank Mordin for letting you down easy. Mordin's response to that gives a little Too Much Information.
It's possible to have Kaidan run into it with Shepard in the first game if Liara is chosen in the confrontation.
Male Shepards can run into this in Mass Effect 3 if they try and hit on Samantha Traynor. Female Shepards can use this to reject Traynor when she tries to seduce her.
Implied in Fallout: New Vegas between Craig Boone and Manny Vargas. When Boone's wife was killed, Manny could hardly hide the fact that he was glad, leading to Boone ending their friendship. Conversation with Manny (particularly if the player has a certain perk) shows that Manny was always jealous of Carla (though her generally unpleasant demeanor didn't win her any favors), though Boone is apparently unaware of his true feelings.
Similar to the Mass Effect example above, Veronica for a male Courier. Then again, a female Courier doesn't have a shot with her either.
Ditto Corporal Betsy.
In the female protagonist's route in Persona 3 Portable, the later ranks of Aigis's Social Link have her lamenting that she's not male and, between that and being a robot, is thus not an ideal love interest for the heroine. Exactly how incompatible she is with the heroine's orientation is to some degree open-ended, but there are no opportunities for the heroine to actively reciprocate her feelings, making it fall more or less into this trope.
Invoked in the "Wedding Day Massacre" DLC for Borderlands 2, where Gaige the Mechromancer admits to having a crush on Sir Hammerlock, but no chance of getting him, since he's only interested in men. She does assert she'd be all over him if ever he became straight.
In Katawa Shoujo we have a failed confession between Misha and Shizune, with the latter being straight.
In Emi's route, Hisao thinks the track team captain will be a rival for his affections for Emi, but it turns out that she once confessed to him, only to find out that he's gay.
The straight pop star Stasia in Marry Me is adored by her lesbian fangirl Parker, who doesn't stand a chance. At an inopportune moment during a concert, Parker hands off her 'marry me' sign to Guy, her male, heterosexual best friend. Stasia is still emotionally unstable from her last breakup, and ends up accepting Guy's "proposal".
PeeJee is established as having this as a near-superpower, up to and including precognition. At one point, one of her ex-boyfriends, a lying scumbag who cheated on her with different women, later comes out as gay after they break up.
A short, three-strip story has Jhim ask out a somewhat mannish woman who looked like an attractive male from behind. He tells PeeJee that they got along really well; if only she were a man! (PeeJee, naturally, is annoyed.)
In Queen of Wands, bisexual Angela has a thing for her straight best friend Kestrel. It becomes a major point near the end of the comic, nearly ending their friendship.
Justin Tolkiberry (a gay male) has Melissa, a straight girl (and his former best friend) who's in love with him and refuses to accept that he's not interested.
Melissa thinks that she can "cure" Justin. Currently, she's in a relationship with Noah. He claims that their relationship is a mutually beneficial one "for close comfort and pleasure". It hasn't been stated outright, but the vibes are that Noah is himself gay, or at least bi, and that Melissa sees her relationship with him as some sort of "proof" that Justin can be "cured".
Susan had a crush on Justin before she learned he was gay. Notably, they're still very close, relate to each other very well, and during the Gender Bender party (which turned Susan into a bisexual man and Justin into a straight woman) they had a heartfelt moment which almost escalated into something they would have regretted.
Justin himself is in love with his male friend Elliot Dunkel, who's straight.
Nanase's relationship with Eliot turned out to be a case of this. Nanase liked him but wasn't really physically attracted to him. When she learned of Sarah's crush on Elliot, she ended the Love Triangle in short order by breaking up with Elliot and admitting she had just been going through the motions. Nanase didn't really consider the ramifications of this, until Elliot accidentally created an Opposite-Sex Clone that Nanase found disturbingly attractive.
Catalina later falls in love with Susan; the latter still wishes to be friends however. Susan even had an Imagine Spot about a date with Catalina, but she's well aware she's straight.
Susan: Could've been nice...
Susan herself expresses 'strangst' (straight angst) in an early appearance, wishing she were a lesbian because of her and her mother's issues with men. (Susan's mother is saddened that her daughter isn't attracted to women. This is mostly due to a traumatic event in Susan's childhood when she discovered her father was having an affair.)
Chad Dracul in Muertitos is lusted after by pretty near every girl in his school, but is himself asexual.
Averted in Arthur, King of Time and Space; although either Tristram or Isolde may be gender flipped depending on the arc, their sexualities will always change to match. Also avoided; in at least one arc, Nimue is a guy, but how this affects her/his relationship with Merlin is never addressed.
In every arc, though, Galehaute's feelings for Lancelot are unrequited, and indeed unspoken.
Rod and Araceli. She's gay, he's a rake. They have a history. Ari is in favor of letting history remain history; Rod wants history to repeat itself.
Araceli and Sherry. Araceli has a secret crush on Sherry, who is straight (at least as far as Ari can tell).
Ménage à 3 has Gary, who loves Yuki. Yuki, while not gay, has... issues with men.
There's also Dillon, Gary's former ex-roommate, who has a gay crush on straight Gary.
In Questionable Content, Tai often complains that of all the attractive lady friends Marten has, he's dating the only one who is into girls. Of course, that doesn't stop Tai from hitting on all the other girls every chance she gets.
And Marten's parents, while still caring about each other, had a case of this when Marten's dad came out of the closet.
Later, Roxy is shown to have a crush on Dirk, who is gay. She knows, or at least suspects, that they're fated to have kids together, and is at least partially interested in the idea. Too bad about the "ectobiological cloning" thing... On the other hand, Dirk has a crush on Jake, who is still considering whether to identify as straight or bisexual.
Later, there's a very heartfelt conversation between Dirk and Jane, where Dirk states that he truly wishes he could give Roxy what she wanted, saying that he really does love her, but not in the way that she wants.
A bizarre inversion in 1/0: So there's never been a fourth wall, and there's very little in the setting except a featureless plain and a bunch of tiny things who chat. Terra would very much like to fall in love with Zadok, but Terra's a lesbian earthworm and Zadok's a male grass golem. She briefly gets a personal fourth wall in order to lose the concept of lesbianism (solely an out-of-universe thing, since none of the characters are human and Terra is the only character with a metabolism), but self-deception is a turn-off for him. The philosopher of the group solves things by successfully arguing that applying the constraints of human biology to people without it is absurd. Love is therefore a function of personalities, and therefore limiting it is a violation of free will and their purpose as characters. Around 1/0, we call this a Tuesday.
Oglaf, being a (very NSFW) sex comedy comic, has this in spades. Recurring offenders are Ambassador Sandoval's desire for strictly straight Ivan the Apprentice, and the various men (and odd shapeshifter) trying their luck and getting shot down by snarky lesbian mercenary Greir.
Heterosexual Jamie and asexual Erin are in love and have a non-sexual romance. Relationship stress ensues when Jamie suffers from sexual frustration, and neither of them wants to have sex with the other.
Discussed at length in Meaty Yogurt with a subplot about a man who cannot get over his feelings for a lesbian waitress. At one point he speculates that finding every woman he likes is a lesbian makes him sorta a lesbian in a man's body. The object of his affections assures him that being a lesbian never coincides with finding every woman you like is a lesbian. Ever. In the history of the universe.
A parody short posits that the reason Sonic the Hedgehog makes such fast tracks when Amy's around is because he doesn't have the heart to tell her he and Tails have long since passed the point of goo-goo eyes. Amy is not impressed.
More than one guy has made passes at Phase in the Whateley Universe. Her entire team always makes fun of these humiliating moments, because her team (and her girlfriend) know that she is really a het guy trapped in a mainly-female body.
ParaNorman: At the end of the movie Courtney decides to stop flirting with Mitch and invites him to a movie. Mitch happily (and completely unaware that she had been flirting with him all the time) mentions that his boyfriend is a Chick Flick nut.
Herman Melville's attraction to Nathaniel Hawthorne.
Mixed-Orientation Marriages of the type where a person who is in the closet about his or her exclusively homosexual identification is married to someone who identifies as heterosexual. Now also called "brokeback marriages" after more recent famous fictional examples.
A depressing fact of life for many a gay person their teen years - they'll usually end up crushing on multiple peers of the same sex before they hit 20 (and maybe graduate from high-school). Given the relatively low numbers of those who would readily identify as gay or bisexual (<10%), at least one of these crushes is likely to be heterosexual and therefore of Incompatible Orientation. Worse, even if the crush's orientation is compatible to theirs 85% of the world's population doesn't live in developed countries where homosexuality is a 'meh'/acceptable thing, so they very probably won't be able to do anything (open) about it due to homophobia. On top of that there's the usual/universal (for all sexual-romantic orientations) problem of the fact that just because someone 'can' have a relationship with you doesn't mean they want to - and even if they do, that doesn't mean you actually have anything in common beyond the love and attraction. Of course, this pattern usually continues into adulthood as well. Depending on the local area and the subculture they're associated with (and especially so in the more homophobic countries/regions), gay people are almost certain to continue having a large majority of exclusively-heterosexual peers in adulthood. If they figure the whole thing is just too much bother and decide to 'settle' for someone of the opposite sex (whom they are by definition incapable of having a real romantic relationship with) it can be pretty awful for The Beard, too, as their love interest is incapable of returning their feelings.
It's also a cliche that straight girls involved in theatre or music in high school will inevitably crush on at least one closeted gay guy.
The dating website OkCupid installed a feature where gay and bi users can keep their profiles from showing up for straight people; one of the reasons was that a lot of straight male users were ignoring this trope and harassing lesbians on the site.