Pictured above is fanart containing three versions of Setsuna F. Seiei from Mobile Suit Gundam 00, however the show lacks any ways to make it actually happen.
Ranma ½: Both the manga and anime explored this, though in different manners:
The anime filler story, which came first, created a female-only (and demonic) copy of Ranma that tried to seduce him to steal his life force, causing him to stumble around zombie-like during the day.
The manga version centered on a haunted mirror, which created identical copies of whoever looked into it. Since the mirror had trapped the spirit of a girl who had longed to have a boyfriend, any resulting copies would then chase anyone of the opposite sex, and try to date them. When a mirror-copy of girl-Ranma was made, she was immediately smitten with boy-Ranma, and she tried to bed him on her very first night of existence. At the end of the story, a male clone was created accidentally, and both copies happily hooked up (since it would take another week for the seal on the mirror to be fixed, whatever they did afterwards belongs in the realm of imagination.
Susumu and Nanako from Homunculus, who have sex with each other after Nanako's trepanation. They each hallucinate their partner as themselves, just with the body of the other gender (but the heads stay the same). This trope is then exploited for creeps over the next few pages in soft-core pornographic detail.
When each Pretty Cure besides Dream is forced to face an Enemy Within while wearing the Mask of Despair. Cure Lemonade faces a creepily affectionate version of her civilian self.
Also, a sticker set for the second season exists pairing each girl up with her implied or stated love interest: Dream with Coco and Komachi with Nuts, both of which became canon in season one; Karen with Milk, which can't be outright stated but is pretty darn close; Urara and Rin with Syrup, both of which are currently implied (but Urara seems to be winning, despite Toei earlier saying otherwise... Rin has bad luck with boys, doesn't she?), and Kurumi with... Milk again. Herself. Yeah.
Happens in the second episode of Kaiba; the woman who helped the title character sneak onboard a spaceship copies her own memories into his body and the two of them have a little fun together... which is quite disturbing given the series' surreal and childlike artstyle. Then the copy kills the original for fear of being deleted.
The relationship between Mukuro and Chrome tends to feel like this. Their names are actually anagrams of each other (in Japanese "chrome" is pronounced "kuromu") note even their last names are an anagram: Rokudo and Dokuro, and they look incredibly similar (other than the gender difference), coupled with the fact that they share a body...
Most people think Tsuna and Kyoko are the closest thing to this without really being related.
Patalliro of Boku Patalliro! has molested and been molested by nearly identical Patalliros of the distant past and future. Presumably they are both ancestors and descendants of the main Patalliro. Let that sink in.
Okay, it never got to "screwing", but in the manga Sailor Cosmos kissed Sailor Moon. Sailor Cosmos is (apparently) Sailor Moon from a Bad Future. Discuss.
Neo Queen Serenity was also pretty excited to see her past self....
In Kaguya Hime, a few characters express interest in the bodies of their clones, but that's (probably) usually because they need their organs. Julian, though, is definitely very interested in his clone Miller; among other things, he mentions having seen an almost-unnoticeable scar on Miller's body during a sex scene in one of the films Miller played in, and later does something that was either nuzzling his face very tenderly, or kissing him (darn you, Discretion Shot). Not to mention the reason he wanted to find Miller in the first place.
The last (non-canon) episode of Kampfer ends with the gender-swapping protagonist married to him/herself. And he/she/they had a child.
The yuri one-shot, Endless Narcissus, is about a girl who loves herself so much she goes and gets a clone of herself.
The opening of Lupin III: The Woman Called Fujiko Mine ends with two Fujikos making out.
In the final volume of Devilman Lady it is revealed that Lucifer reincarnated himself into this world as a sister and brother (who changed his gender to hide himself), then had sex with him/her/themselves, became pregnant, gave birth (within hours of the act), then fused back into one hermaphrodite self - all of this to give birth to a man who was his beloved in previous life... Yup. It must have been made on drugs.
In one bit, stand-up comedian David Cross jokes about this guy at the gym fantasizing about pulling himself out of the mirror, and the two thems dance to Barbra Streisand music, make out, and then "they fuck each-other on the Flexinator 500!"
In a broadly similar vein, Woody Allen once quipped: "I love to masturbate. It's sex with someone I love."
A common joke: "My own clone! Now neither of us will be virgins!"
In one of Jim Gaffigan's specials, he says couldn't have sex with another man, "unless he looked like me." "Jim-on-Jim" action, indeed.
Jamie Madrox (a second-string X-affiliated character) has the power of self-duplication, which allows him to split into multiple physical copies of himself, sometimes with distinct personalities. Guess what trope comes up in about 90% of Madrox-related Fanfic. One of Madrox's duplicates brings out the subject when he's sitting bored at a bar. He indicates he'd rather continue to be bored.
An unusually blatant example, The Sentry and the Void are both alter-egoes of the same man, split into two bodies, who have passionately kissed on at least one occasion. Void tells Sentry he loves him and then aggressively tongue kisses him. Sentry responds by tossing Void into the Sun!, so he obviously didn't enjoy it.
XXXenophile delved into the trope more than once, with stories titled "Self Indulgence" and "Dopplegangbang", clones in "Family Reunion", and a situation in "Heart of Stone" where a cleric has to turn two of her fellow party members into illusionary duplicates of herself in order to satisfy the conditions of a curse.
Once he discovers that the Jaeger-monster is the Anthropomorphic Personification of his anger, Finder's Magri White declares that he can do as he pleases with him, and proceeds to play tonsil hockey with him.
Deadpool once went to another dimension where he encountered a female version of himself and they made out. He then declares Squick.
In Little Ego (an erotic parody of Little Nemo), Ego has a dream where her reflection steps out of the mirror and starts to have sex with her. Then the reflections of both of them step out of the mirror and join them. And then the reflections of all four. And then she wakes up.
In Green Lantern comics, the title character's girlfriend, Carol Ferris, was once possessed by a creature made entirely out of love called the Predator. He gave her a Literal Split Personality, in this case separating her masculine side from her feminine side. His ultimate plan was to achieve this trope, but it didn't work out, largely because the male version of Carol turned out to be a creepy stalker.
The Ultimate Spider-Man version of Spider-Woman is a female clone of Peter Parker who has all of his memories. As she and Peter are about to part ways, the two of them share an "awkward hug".
Ultimate Spider-Woman: For the record, I'd regard it as masturbation. Just saying.
This may not be a literal application of the trope, but when Most Excellent Super-bat of the Super Young Team met a young woman cosplaying as him, he felt he couldn't pass up the opportunity to get with her. He claims it was the simple fact that there are people out there who practically worship him that got him so turned on, but it's hard to not see it as an exercise in narcissism.
In the 2011 Dollhouse Epitaphs mini-series, an Ivy imprint in a male body and an Ivy imprint in a female body are seen hooking up, though Alpha (with whom the Ivy imprints are trying to raise an anti-Rossum army) interrupts them before they can get fully undressed.
Pick a film/TV series. Guaranteed there's at least one fic out there of a character screwing a different character that actor has played. Which is sort of like screwing yourself.
The fandom wound up with this due to the actor for Tom Paris having been on Next Generation as an entirely different character. So a lot of fanfic winds up with the two characters meeting up in some bar, drunk. (Or, alternatively, just doing a Recycled Script of someone else's fic with Tom being such a narcissist he heads to the holodeck to copy himself.)
Then there is all the times Voyager crewpeople have met duplicates of themselves. Or not met the duplicates of themselves. They really do give the actors lots of roles to play.
Although never even hinted at in-series, the use of "regeneration" in Doctor Who and the propensity for the Doctor to meet his past selves has all the inevitable implications. There is even an entire livejournal community dedicated to exactly this. There are so many works devoted to relations between the tenth Doctor and the copy regenerated from his preserved hand that they have their own trope name: Tencest.
Any character with a split personality (especially where the other half is a Bishōnen), such as H/Allelujah from Mobile Suit Gundam 00, D.N. Angel or Yu-Gi-Oh!, will be given this treatment in some niche of whatever fandom the character appears in. Explicitly, said "characters" in one body (like Allelujah and Hallelujah) will instead be two separate characters all together, and... will make music together. And this is not restricted to anime.
Especially Yu-Gi-Oh! Perhaps the most popular pairing in the fandom is Yugi and Yami. Add in Yami's past self Atem for a threesome. There's also Bakura and "Ryo", and Marik and "Malik", fanon names for the evil and good sides of the characters. Kaiba and Set (his past self) is also popular.
The Yu-Gi-Oh! GX fandom has something called Monochromeshipping, which pairs up Season 3 Manjuome Jun with... Season2ManjoumeJun (however, in most fanfiction, whatever happens between the two Juns happens purely in his head.) Judai×Haou and Johan×Possesed!Johan are also fairly common.
Lavi and Deak from D.Gray-man. Also, Allen and the Fourteenth Noah. And I've actually seen a fic where Allen was paired with his innocence.
The title character of Naruto is technically able to create a clone of himself — of the opposite gender to top — and the fans haven't ignored its potential. It's called the Harem Jutsu for a reason.
Ranma ½ lemon fics use this with Ranma's male and female sides. Some would say far too often; others would say not often enough.
And it's not always strictly with Ranma(s); for example, there is this Nabiki×Nabiki lemon fanfiction entirely about this trope: Narcissism.
There is one Mind Screw fanfic where it is revealed that, thanks to some Time Travel, Ranma is both is own father and his own mother....
There's two actually. One where he's actually both Genma and Nodoka... and another where he gives himself up for adoption to the Saotomes.
This can be argued as the case of the fanshipping of Luc and Sasarai in Suikoden. While they are Polar Opposite Twins in terms of personality and their canonical relationship more closely resembles Cain and Abel, the fact that they are cloned Artificial Humans of their father means that they are genetically identical, making any pairing with them riding the line with this trope.
Youko Kurama×Shuuichi Kurama is seen occasionally in YuYu Hakusho fanfic, but they're not usually portrayed as the same person.
There is a really bizarre (pun completely intended) JoJo's Bizarre Adventure lemon which included Will×Gyro and Jonathan×Johnny pairings. May or may not count though as Gyro and Johnny are their alternate universe incarnations, but look and act very different.
There's William T. Riker's transporter clone W. Thomas Riker, who has the advantages of being A) one of the vanishingly rare Star Trek duplicates who is not remerged, killed, or returned to his home universe at the end of the episode, and B) Jonathan Frakes.
Goatee!Spock from the Mirror Universe is the other major example of a duplicate character left kicking around after his episode. Considering that Spock is one half of the pairing that originated the term Slash...
Not to mention Nu!Spock×Spock Prime on the Star Trek Kink Meme. Oh, yes, it's happened. But after all, this is thekinkmeme we're talking about. There is also Nu!Kirk×Kirk Prime, and possibly others, but the two Spocks do have the advantage of already being in the same universe.
Supergirl has an alternate-universe doppelganger named Power Girl, who is basically her, only ten years older and more aggressively individualistic (she doesn't wear Superman's costume), with shorter hair and... well, if you've ever heard of the character, you know what else. There is a(n un)surprising amount of Supergirl×Power Girl slashfic.
One of the well-known example is Tea of Sagittarius series, where the original Kyon is accidentally genderbent into a female version, which made Haruhi almost freak out in happiness to the point that Mikuru and Itsuki suffers same fate. Long short story, Haruhi unconsciously summons male Kyon from another world as well. Regadless, out of curiousity, pride, and self denial they began to explore the world of sexual perversion in secret, taking advantage of their current state and both insist that this would count as masturbation instead. It wouldn't be so bad if this ISN'T about Kyon & Kyonkowe're talking about, as someone commented:
In Kyon: Big Damn Hero, Kyon has a dream involving Mikuru and Adult!Mikuru but stops thinking about it before it goes into any detail.
There is a Code Geassslash fic where Zero and Suzaku are fighting over Lelouch's affections. The author has also written other stories involving Zero/Lelouch and has admitted in one of her other slash fics that she asked FanfictionNet to add Zero's name to the character list for the sole purpose of writing these types of fanfiction.
Somehow, there are Danny Fenton×Danny Phantom pairing fan-works, even though it's impossible because he's one person... Unless you count the thing with the dream catcher that can split him into two halves twice.
There's always the fact that one of his powers is actually creating duplicates of himself. And yes, one of the duplicates can go back to human with the other staying as ghost. Granted only Vlad and his Bad Future self did that, but it's only a matter of training for Danny to do it.
Ever since Tomb Raider: Underworld, there's been an increasing number of pics with Lara and her Doppleganger from that game.
ThisGargoyles fanfic features multiple clones of Anton Sevarius, some of them gender-swapped, and the daughter that one pair among them decided to create the old-fashioned way as an experiment. (Note that this story occurs more than halfway through an extensive fanfic continuity.)
And Linkara×Mechakara. As you can probably tell from how Mechakara is in canon, it's also insanely disturbing. Technically Mechakara only looks like Linkara as part of a disguise. Proper selfcest would be Pollo×Mechakara.
One Sailor Moon fanartist and fanfiction writer, Bill K., lets Sailor Pluto have some fun this way, with several time-traveling future selves.
The Kingdom Hearts series has a strangely huge potential for this (and don't think for a second fandom hasn't picked up on this), with Riku and the Riku Replica, Demyx and his waterclones, Xemnas and Xehanort's Heartless (heck, why not Xehanort himself?), Roxas and Sora, Kairi and Namine, and most recently, Sora and Xion. And Roxas and Xion. And Sora, Roxas, and Xion, for a threesome of selfcest.
There is a good chance the whole Roxas, Sora, Xion thing could go even further with Ven, who undoubtedly is in some way "the same being" as Sora×Roxas×Xion, given his appearance and voice being absolutely identical to Roxas'. So now we have foursome potential, although this assumes they can all co-exist, but we don't know yet for sure if that can potentially happen. And Vanitas makes five.
There's also the innumerable stories and drawings which pair the Squaresoft Expies from Kingdom Hearts with their original inspirations.
Just for a compelte list: the past and present versions of Mickey and Pete, Vexen and Vexen Replica(s), Sora and Anti-Sora, Roxas and Shadow Roxas, Donald, Goofy and Sora's Master Form (technically), Roxas and Ven, Vanitas and Ven, the real and virtual versions of Hayner, Pence, Olette, Seifer, Vivi, Fuu, Rai, Setzer and Kingdom Hearts itself. In Final Mix, there's the real and virtual versions of everyone in Organization XIII, and Larxene and Zexion's copies...
Diego Armando×Godot. The game had some people believe that Diego and Godot are twins, at least before the reveal. The obvious difference in their looks was explained with partial albinism, which is known to cause problems with eyesight along with the obvious white hair. And as no-one knew what colour Godot's eyes were and fangirls are prone on jumping the gun...
''Sheik×Zelda is popular. Tetra×Zelda, less so for some reason. Tetra×Sheik practically doesn't exist (and technically doesn't count).
On the other hand, surprisingly little The Legend of Zelda: Four Swords hentai exists. But why write selfcest when the official manga itself is already catering to the pairing (Red×Blue Link, to be specific)? Freud would love to read that one.
Dark Link and regular Link (of any game/universe) are paired together so often it long ago stopped being funny.
There is fanart of Wind Waker Link and young Ocarina of Time Link. Also of Twilight Princess Link and adult Ocarina of time Link. And for the ones who want to cross over to Shotacon territory, there's always a combination of the two... including both versions of Ocarina of Time Link together. However, the only one of those that is Screw Yourself is the Ocarina of Time Links, as the others are just expies, identical great-great-(etc)-grandson, or Generation Xerox.
The 2012 movie version of The Lorax had only been in theaters less than a month before the internet was swarmed with fanart/fanfiction/fanWHATEVER between the Young!Once-ler and The Onceler, nicknamed "The Greedler" (after he becomes successful). The cute little pairing name for it? Oncest.
Oncest, nothing. The Lorax fandom has elevated this to an art form, with Tumblr blogs consisting of every possible AU and personality for the Onceler, and all of them are shipped together. At this point it's no longer the Lorax fandom, its the Onceler fandom.
Breath Of Fire IV (unsurprisingly) has a prodigious amount of Fou-lu×Ryu fanart and fanfic — to the point that this pairing has earned not one but twoFan Nicknames: FouRyu and Yorae Dragon Masturbation Fanwork. This is only encouraged by the fact that the two are a Literal Split Personality and that there is a manga adaptation ongoing in the same manga magazine running Vassalord. By the same company that was responsible for Peacemaker Kurogane. If this isn't brain-breaking enough, consider that Fou-lu is strongly implied to have a romantic interest with a woman who cared for him and ultimately was murdered in an attempt to literally nuke him, leading to the Fan Nickname of FouMami for the second most common pairing in the BoF IV fandom. And yes, there is a decently large chunk of the Japanese fandom in particular who writes both FouMami and FouRyu. Particularly involving comfort selfcest.
Vocaloid fanfiction and fanart tends to use this trope, mainly because the fandom likes creating Opposite Sex Clones of the official characters. A favorite pairing is Len×Rin, which tends to overlap this with Brother-Sister Incest. And even they have their own fanmade gender-swapped clones.
In many, many, MANY Power Rangers SPD fics, the fact that Z can create duplicates comes to the fore for just such a reason.
Tommy Oliver is sometimes paired with his clone/ancestor Tom. There's even a few fics that are threesomes of Tommy, Tom, and the White Stranger.
Death Note fandom has a small but dedicated contingent which ships Kira Light with mindwiped Light, in an Enemy Within-style thing.
Axis Powers Hetalia: Himaruya's liberal use of opposite-gender counterparts and AUs in his own work, along with the possible nature of civil wars and so on, has led to some selfcest fics.
One increasingly popular fanon pairing is Prussiacest, which basically pairs Prussia either with a copy of himself or his Nyotalia counterpart. The logic behind it being that only Prussia is awesome enough to be with Prussia.
In one Calvin And Hobbes arc involving time travel, Calvin and his future self both end up taking off in the time machine leaving two Hobbeses alone. There's at least one comic floating around the Internet that... um... focuses on what they get up to in the meantime. Brain Bleach is mandatory.
There is a fic (NGE: Bloodlust, chapter four) including a scene where a clone vampirificates another and the two celebrate the occasion by playing with each other.
And another one where Rei gets bored during class and starts fantasizing about her being replaced by one of her clones without her being told about it. Since one of them has to be eliminated, they hold a lesbian version of a last supper...
What does exist involves interaction between counterparts from PC-98 and Windows continuities, the canon doppelgangers in Phantasmagoria of Dim. Dream, and the characters who can use body doubles to attack (especiallyYuuka and Flandre). Or Yukari could just be fooling around again.
Youmu (a half-ghost with a one human and one ghost body) can pull it off with or without magic, and it's been done to various degrees. And remember, in canon her ghost half can be altered into a copy of her human half. We will leave the rest to your imaginations.
Professor Layton rarely (since the ship has a Shotacon nature) but still has the two Lukes of the third game, the little!Luke who is familiar to anyone who keeps up with the series, and his future self: big!Luke. Subverted when you discover "future Luke" is a sham.
There's also Giving Love a Helping Hoof, which has the mane 6 meet their male counterparts because of an anomaly in the Elements of Harmony, forcing Princess Celestia to create male versions of not only the mane 6 but Luna and herself as well to keep the balance in Equesria (and Solaris and Artemis just for the heck of it).
There's a considerable amount of fan art and fan fiction that turns Trixie's narcissism as seen in the show Up to Eleven. Much of it involves either Trixie fantasizing about herself with the aid of a mirror or using clones produced through magic, but in one parody fanfic she ended up having a 5-way with her reflection, a clone, a future version of herself, and a robot with her likeness. And to further complicate things, the story closed with a male version of her from a parallel universe walking in.
And then we have "Perfect for Me", which is part hilarious, part bizarre. It's about Twilight creating a clone of herself to help solve a series of time crunches. Then the Twilights start to fall in love with each other. Yeah, it's a strange story.
Persona 4 fandom: Shadow-on-human action? There's a pretty huge chunk of Yaoi Fangirls who will slash Yosuke with himself, or Kanji with his Armoured Closet Gay, or Teddie with his nihilism, or even the MC with his shadow, though he never had one... And, of course, people with other people's shadows, or others' shadows AND the human, out of some forced yet plausible Twin Threesome Fantasys. This all applies to the girls too (such as Chie and Dominatrix Bananahead), but it's just more prominent among Yaoi Fangirls. On second thought, it's not so much screwing themselves rather than aspects of themselves... but we'll save the philosophical implications for another day.
Naoto×Shadow Naoto is one of the more popular Human×Shadow pairings.
And its predecessor Persona 3's most popular yaoi pairing is Minato×Ryoji. Take note that Ryoji is supposed to be a part of Minato. This also applies for Ryoji×Female Protagonist shippers.
Or Minato x Female Protagonist
Since her creation in Phase 3 of Gorillaz, Cyborg!Noodle has naturally appeared in fanarts where she's making out with Real!Noodle.
When Dante in Devil May Cry 3 gained the Doppleganger ability, it gave the fangirls an excuse to do this. Not that Dante didn't have enough problems already, given that he has Vergil pestering him.
Starcraft: An artist on deviantART was badgered into producing this image involving Zergified!Kerrigan and Terran!Kerrigan. For all intents and purposes she seems quite disturbed by having actually drawn it.
Quite common in Homestuck fandom, particularly with the Time players whose powers include Stable Time Loop formation. Dreambubbles allow characters to contact alt-universe dead versions of themselves in their sleep. With the way the trolls' Bizarre Alien Biology works, ancestor/descendant pairings may or may not have hints of this, though it's closer to incest; ancestors and descendants are born centuries apart and happen to have very similar genetic makeup.
Adventure Time has an in-universe Rule63 known as "Fionna and Cake", which also happens to be in-universe fanfiction. One of the most common ships is Finn with his counterpart Fionna, though Bubblegum/Gumball and Marceline/Marshall Lee are common pairings. No shipping of Finn/ Ice King! Finn, though.
A deleted scene in Austin Powers: The Spy Who Shagged Me has Number 2 from the past and future in bed, smoking cigarettes, and the older one musing that it's not technically cheating. This is based on the gag actually used at the end of the movie, with two temporally displaced versions of Austin ending up in bed with his Love Interest.
Austin: Paging Dr. Freud!
Star Trek VI: The Undiscovered Country: Kirk to fellow Klingon-gulag inmate Martia, who turns out to be a shapeshifter, formerly in the form of an attractive female humanoid and now in the form of Kirk himself:
Kirk: I can't believe I kissed you! Martia: Must have been your lifelong ambition!
In The6th Day, Adam Gibson, who was cloned without his knowledge, tells the villain he should clone himself while he's still alive. The villain asks if it would be so he could get Adam's unique perspective. Adam says, "No, so you can go fuck yourself." (and when the dead villain falls over an unconscious/incomplete clone of himself, Adam's reply is "When I said you should screw yourself, I didn't mean it literally.")
The John Waters movie Female Trouble stars a character played by Divine who gets raped and impregnated by a man... who is also played by Divine. She ends up homeless and she calls her baby daddy for help.
In several film adaptations of Dr Jekyll And Mr Hyde, Jekyll and Hyde hallucinate each other and so are able to interact. Usually they fight or argue, but sometimes their actions can get a bit... suggestive. Rather appropriate given that one of the possible literary interpretations of the book is as an allegory to the double life that was necessary for Victorian-era gay men.
The 2002 John Hannah adaptation is a prime example of this, with Hyde often getting intimately close to Jekyll, and even licking him on the cheek at one point, and in the 2008 film starring Dougray Scott, at one point Hyde pins Jekyll to the wall and kisses him. That's the farthest that any movie adaptation has ventured to go, but several fanfiction works have taken this idea even further.
F.M. Busby wrote a short story with a similar concept using Reincarnation instead of a Gender Bender. The hero dies and finds himself reborn in the past as the girl who will eventually become his beloved wife. He/she then gets to re-experience their life together from her perspective, eventually giving birth to a daughter who turns out to be (surprise, surprise) him/herself yet again, reborn once more into the past.
Fifteen-year-old Henry finds an outlet for his pubescent sexual urges this way (and, it's implied, repeatedly) in The Time Traveler's Wife. For added fun, his father walks into the room and catches him (them?) in flagrante. Henry rationalizes having gay sex with himself as a parallel to masturbation, and the obvious course of action that "anyone" would take in his situation (thankfully, his eponymous wife never needs to hear about it). Note that possibly they were only jerking each other off. And the father walks in on them post whatever-happened, although it was still totally obvious to him that it was something sexual.
Parallelities by Alan Dean Foster not only has the main character bedding an alternate female version of himself while traveling through The Multiverse, he eventually finds an alternate Earth populated entirely by doubles of himself.
The Darkover novel Two to Conquer has the main character meet up with an exact physical duplicate of himself. The expected interaction occurs.
While the book doesn't get that far, in Magyk by Design by Esther Friesner, a cat (talking, magical) named Scandal gets split up into a number of copies by villains (who can control the copies). By the end of the book, he reabsorbs them. Except for the one representing his female side, who being just a kitten was useless to them and out of the fight. He's accelerating her maturation, for this trope's purpose, with her full encouragement. (They are the only two cats in this world...)
"Nine Lives", an early Ursula K. Le Guin story, has a set of ten clones, five male and five female, who join some place where there were already two normal people working. When the clones have sex with each other, one of the non-clones says, "Oh, let them have their damned incest!" and the other says, "Incest or masturbation?" (The clone-sex wasn't a major plot point, just a part of showing how the clone-group couldn't relate properly to outsiders.)
A similar case of clone incest appears in John Varley's Titan, where the lab-cloned Polo sisters privately engage in behavior that's still illegal in Alabama.
Varley's stories have often had this, including The Phantom of Kansas.
Used romantically with several pairings amongst the Starfish Characters in Scorpion Shards. They are soul mates, so to speak, but it gets a little weird when one of them realizes he can't fall in love with someone who isn't part of the group.
The main character in James Alan Gardner's Commitment Hour spends the last few chapters of the book having "impure" thoughts about a female clone of himself. To make matters worse, their minds are linked to share memories between them, so she "hears" every one of the thoughts. And likes them. The end of the book strongly implies the the character ends up romantically involved with his own clone, while a third, hermaphrodite clone has a whole 'nother squick going on.
In Frederik Pohl's The Coming of the Quantum Cats, similar characters from a mulititude of timelines mix & match during a cross-time war; when a slightly more advanced timeline decides to quarantine the others to avoid eddies in the space time continuum, a lot of editions get dumped on an uninhabited Earth, where multiple copies of a particularly unsavory mook decide to set up house together.
In With a Tangled Skein, Niobe kisses two alternate timeline versions of herself. Clearly justified, as Niobe is essentially described repeatedly as the most beautiful woman of her generation.
The short story "Blood Sisters" by Joe Haldeman involved the Mafia cloning a young heiress in order to substitute the clone and get the inheritance. The clone didn't want any part of the plan — she thought of the original as her mother and didn't want her murdered — and went to a private detective to ask for help hiding from the Mob. When she finally met the heiress, however, the mutual attraction was strong enough to overcome any qualms about being intimate with her mother. The detective comments, "I did wonder what you would call what they were doing. Was it a weird kind of incest? Transcendental masturbation?" At the end of the story, it's mentioned that original and clone openly being lovers "started a fad among the wealthy, being the first new sexual diversion since the invention of the vibrator."
A strange case in Sergey Lukyanenko's Autumn Visits, where Anna has a "shower moment" with her not-quite-human duplicate Mary. It's not specified exactly what they do in the shower, but their mutual attraction is clear, although Anna's attraction is mostly due to religious fervor (she believes Mary to be God).
Isaac Asimov wrote a parody of "Home on the Range" called "Home with my Clone" ("...with the Y chromosome turned to X.")
In Redshirts, the main characters get the actor playing one of the stars of the television show they're characters on to help them when the character he plays seduces him.
In "A Clone at Last", a short story by Bill Pronzini and Barry N. Malzberg, a man who has little luck with women commissions a female clone of himself. He waits until the clone is eighteen years old before he tries to seduce her to avoid being arrested for statutory rape.
In the book Goldfinger, when he has captured Bond and expects him to talk (also to die), Bond steels himself, telling him "you can go ____ yourself." Goldfinger good-naturedly replies "Even I am not capable of that, Mister Bond!"
In "Parallel Universe", the crew goes to a parallel Red Dwarf where humans are all of opposite genders, and Lister gets drunk and sleeps with his female self, to the disgust of both versions of Rimmer.
The parallel universe has male and female roles completely switched, so Deb Lister gets Dave Lister pregnant. This is revealed immediately before the end of the episode, and what happens to the fetus is dealt with in some fast scrolling text at the start of the following season....
In this same storyline, the Cat is very excited to meet his female opposite and is clearly planning to have sex with her. "If you hear me screaming, do not, I repeat, DO NOT come to the rescue!" Of course, his opposite turns out to be a male dog.
Ironically, in "Rimmerworld", he decides to make an Opposite-Sex Clone of himself... somehow. And then have sex with the clone, despite some misgivings:
Rimmer: This of course created the most enormous moral dilemma. Technically, she would be my sister, and therefore unable to take me as her lover. After much soul searching, I reluctantly decided, "What the hell", I just wouldn't tell her.
He fails, of course. However, the resulting male clone does not, and goes on to eventually create and entire population of "Rimmers", both male and female. Even more disturbing is the fact that their cultural rules require execution of anyone who does not meet the exact physical and moral attributes of the original Rimmer. Although for the women, this means facial features only... which really isn't any better.
In the episode "Camille", they met a Gelf who appeared to each character as their "perfect companion", which everyone assumed to be their perfect female companions. Predictably, Lister saw Kochanski (or rather, Kochanski if she was a bit more like him, including Scouse accent); slightly less predictably, Rimmer saw a fairly plain, underachieving hologram; and Kryten saw a robot which looked very similar to him (because they're from the same series, series 4000), but had a distinctive personality and looked slightly more feminine. The Cat, after much excitement, finally sees himself.
Cat:I'm the object of my own desire?! Gelf Cat: Can you think of anyone more deserving? Cat: Well, when you put it like that, I guess not! Damn my vanity!
Perversions of Science used this concept. A man decides that no woman is good enough for him, so he decides to create "the perfect woman" by having a sex change and then going back in time to have sex with himself.
A skit on The Man Show had Adam Corolla and a clone of himself, eventually coming to the conclusion "After all, it's only me, right?"
This was also brought up in the episode where Xander was split into two Xanders, though the comment was about a threesome with them and Anya. The other Xander in that scene was being played by Nicolas Brendan's identical twin brother, so there could have been some Twincest there as well.
Well, Alex from Wizards of Waverly Place doesn't meet herself and make beautiful music, but she still falls in love with herself when she drinks both halves of a love potion. The bad part is that her head gets big whenever she compliments herself... literally big.
When he is forced to accompany Adelle to the Washington DC Dollhouse, Topher imprints Victor, a blank active, with his own personality in order to mind the shop in LA. This leads to the following exchange over the phone:
Topher: She's got me locked out on this end. Victor!Topher: Who's your back door man? Topher: We'll pretend I didn't say that. Victor!Topher: Yeah.
One of the ways the illusion-casting Candice from Heroes tries seducing Sylar is by appearing to him as Sylar. ("Or something more familiar... if that's what you're into.")
Subverted on Scrubs: J.D. thinks that his girlfriend, Dani, moaned her own name during sex, but it was actually the guy she was seeing at the time, whose name is Danny. He's also the Soup Nazi.
In Sliders, Quinn once discusses his adventures on a talk show, and mentions having met a female version of himself. He is immediately asked, "Did you have sex with her?" (We never really found out if he did, though they did kiss. She was Ax Crazy, anyway.)
At the end of the new series' season 4, three versions of the same Doctor are formed: the Doctor proper, the Clone Doctor and the DoctorDonna. Captain Jack, when finding out that "there are three of you now?", says "I can't tell you what I'm thinking right now."
And speaking of Captain Jack, it was hinted at in "Utopia" that, as a result of his immortality, he could find a version of himself even at the end of the universe... and then when Jack seems to consider this, followed up with the line that it would be the "only person you'll ever be happy with..."
The 2011 Comic Relief special has a timeslipped Amy Pond. If they don't act carefully the slip will stick and they will be stuck with two Amys, and when asked what he would do then Rory "has a few ideas". Later on, Amy and Amy start flirting with each other.
In "A Good Man Goes to War", the 2011 mid-series finale, River Song strongly implied that she once spent a very enjoyable birthday with two different versions of the Doctor. Lucky girl!
Stargate SG-1: Given how much puppetmaster Ba'al was hitting on Adria, what he might have had in plan after one of his clones possessed her may have fit the trope. However, he never got to carry on his plans, so we may never know... which is probably best.
The writers of the show at the time of that episode have revealed that this was meant to be purely Mirror Kira being extremely self-absorbed, but later writers interpreted it differently and they have shown her in another lesbian relationship when revisiting the Mirror Universe
"Facets" reveals that Curzon fell in love with Jadzia when he was mentoring her; they end up joined to the same symbiote, becoming a retroactive version of this trope by way of The Nth Doctor.
Mystery Science Theater 3000 references this trope a couple of times, once when talking about a Time Travel movie (Time Chasers), and once where a character is in a computer simulation with a copy of himself (Overdrawn at the Memory Bank).
Rob Brydon's onscreen kiss with Ben Miller on QI after an episode's worth of jokes that they were identical.
Ben: So that's what it's like! Rob: Now I know why my wife married me!
Robin from How I Met Your Mother honors this trope as well. Once she gets back from Argentina, she undergoes an identity crisis while talking a lot, in her dreams, to her vacation double. When Robin is finally herself again, she mentions that "vacation Robin" popped up in her dreams again and they went all the way.
Tony has sex with Beth in his series 2 episode of Skins. Possibly. Beth is either a figment of his imagination, an aspect of his personality (his long-lost anima), his sister, himself, a completely random person, or — most likely — all of the above.
The incredibly self-absorbed Jenna starts dating a celebrity female impersonator of herself. It's about as close to this as a heterosexual woman can get without the benefits of advanced technology.
In the episode where Tracy buys a "Japanese Sex Doll" of himself, Jack asks him why he would make such a purchase "other than the natural inclination to make to love to yourself".
During the 100th episode, while everyone is hallucinating, Jack is visited by three versions of himself from his past, an alternate present, and his current future. After he resolves his existential crisis, the three of them stand around and decide that the only rational option is to go have sex with each other.
In one episode Hannah Montana, after seeing a picture of herself as Hannah Montana photoshoped to make her look like a guy, Miley comments that she would totally date herself.
In the Queer As Folk second season finale, Brian fucks the actor who played a superhero based heavily on himself. This is the catalyst for Justin leaving him.
Michael: You didn't have to walk out on him like that in front of everyone, you know. Justin: I would've told him to go fuck himself, but he was already doing that, in the back room with Rage.
An episode of Nip/Tuck features a wealthy older gay man who hires the plastic surgeon protagonists to reconstruct the face of his young boyfriend to resemble a younger version of himself.
At the beginning of the third series premiere, new character Rudy mentions that he would definitely have sex with himself if he could. Bravado maybe, but thanks to his power he actually can.
While it may not involve actual sex, it probably still qualifies as selfcest — after Curtis gains the power to swap genders he ends up getting himself pregnant by "cleaning up" with the same tissue first as a man, then as a woman.
the first time (with Jason Sudeikis as his younger self and his older self) played it straight and briefly conversed it (Sudeikis's older self tells his younger self that "It's not gay" because "I'm you" and asks him if he ever wondered what it would be like to have sex with yourself, which convinces his younger self to go through with it).
The second time (this time with Bill Hader as his younger self and a disgusting, overweight version of himself in about two years) plays this for Black Comedy (with some hints of Crossing the Line Twice) when, after his overweight, disgusting future self tells him that he'll end up fat from too many steak dinners, broke from blowing all of his money, and on a plane to Hawaii where he'll "disappear" *
i.e., commit suicide by putting a gun in his mouth and blowing his brains out
, the overweight future self tries to rape his younger self (with his younger self shouting, "No, no, no, no!" and trying to fight him off).
The third one had Ben Stiller mistaking a woman (Abby Elliott) sitting next to him for his future, transgendered self — until his actual, future transgendered self tells the woman that the man was talking to her.
Taken to a much more ridiculous extreme in the video for "You And I", where her lover's role in the video was played by herself in her drag alter-ego, Jo Calderone. She also performed the song live as him at the MTV awards.
I've always kind of been partial to calling myself up on the phone and asking myself out. You know... (whoops from the audience) Oh yeah, you call yourself up too, huh? Yeah... Well, one thing about it, you're always around! Yeah, I know. Yeah, you ask yourself out, you know. Some class joint somewhere. The Burrito King or something. You know... Well, I ain't cheap, you know. (...) Well, usually about 2.30 in the morning you've ended up taking advantage of yourself and... there ain't no way around that, you know. Yeah, making the scene with a magazine, there ain't no way around... I'll confess, you know, I'm no different, you know. I'm not weird about it or anything. I don't tie myself up first.
Rammstein's "Zwitter"; sung from the perspective of a hermaphrodite who is in love with him/herself.
"Ich bin alleine doch nicht allein, ich kann mit mir zusammen sein" (I am alone but not alone, I can be together with myself)
The lyrics are explicit about this trope:
"So bin ich dann auch nicht verzagt, wenn einer zu mir "Fick dich" sagt" ("So I'm not sad even when someone says "fuck yourself" to me.")
Schaffer the Dark Lord's "Attack of the Clone Fucker".
The video for "Sober" by P!nk features Pink, in naughty lingerie, making out with... another Pink in other naughty lingerie. Take a look here. Starts about 2:20 and gets intercut here and there nearly to the end.
The music video for "The World Is Not Enough" by Garbage has the robot double of the lead singer killing the real singer (Shirley Manson) by kissing her.
The video for the Björk song "All is Full of Love" counts, right?
A scene in one version of Janet Jackson's "Together Again" video has Janet Jackson leaning her face and hand on the breast of another Janet Jackson who is wearing a strategically pixelated transparent top.
Cat Rapes Dog's song "Adore Myself" is about either this or regular old narcissism.
Dave Grohl of Foo Fighters in the video for "Learn to Fly". Twice. A pigtailed girl played by Grohl has a crush on Grohl As Himself, and the Camp Gay flight attendant flirts rather suggestively with the pilot, both also played by Grohl.
The Bible: This trope goes right back to Adam and Eve, if you believe the whole rib thing (or, respectively, if you take it either literally or the wrong (?) translation. There are some who interpret the Hebrew word as "side" or "aspect" and say, that Adam was a hermaphrodite in some way and the God took the female side/aspect and made it into a seperate being). And then there are the interpretations that suggest she was made from a different bone entirely, one present in many mammals but not in humans.note Specifically the baculum, which is a bone in the penis to help with copulation. Humans do not have them, and function entirely hydraulically.
The player's handbook to Aberrant (a White Wolf RPG centered around people developing superpowers as a world-wide phenomenon) contain a chapter with various superhero teams and similar groups across the world (some of which are painfully ethnic). One is the Queer Nova Alliance, an informal group of Novas (superpeople) with "alternate lifestyles". One member is Tommy Orgy, whose selection of powers includes self-cloning. Or, as another nova observes, "Gorgeous, gay, and able to duplicate himself; its a wonder Tommy Orgy ever leaves his house." When Tommy tells another nova to "Go fuck yourself", the other retorts, "I thought that was more your forte, Thomas." A listener adds, "Well, according to every other fanfic I read on the OpNet, anyways..."
There are a number of ways to go about this in Mage: The Awakening. Shapeshifting lets one person take the form of another, but it's also possible for a mage to divide into two or more bodies. The more esoterically inclined can journey into their own minds or cause aspects of their personalities to manifest physically: there's a mention of a mage who incarnated their own lust. Archmasters can create avatars; meet past, future, or alternate-timeline versions of themselves; and do it all in worlds generated from their souls, where they are aware of everything happening within. Power Perversion Potential indeed.
In Metal Gear Solid 3, dress Snake up to look like Raikov, stand in front of Raikov, and just wait.
In the same series, the ridiculous levels of Foe Yay between Solid Snake and his "brother" Liquid Snake.
Then there's the marketing campaign for Metal Gear Solid: Peace Walker, which so far seems to be furiously attempting to encourage this as much as possible. The first trailer alone depicted four Big Bosses, and at the end they got in a pink box (labelled "LOVE PACK") which jiggled suggestively, alerting a nearby guard. The second trailer involves soldierly Ho YayCPR and masculine hand-holding and dialogue about always sticking together, between two Big Bosses. Whether this becomes part of the game or not remains to be seen, but Hideo Kojima is at least having fun with it.
It's now been revealed that a) the four demo-ready character builds are all different versions of Big Boss, and b) the Love Box is indeed a two-person cardboard box and that if two Big Bosses stay still in it for too long, it will start to jiggle around. Not surprising, as even the guys want Big Boss, and that includes Big Boss. The official website gives an innuendo-filled description of the Love Pack, saying 'in the spirit of camaraderie, some may find it comfortable!'. And also reveals that the characters giggle when taking items from each other, because it tickles. Big Boss is officially the gayest thing in an already incredibly gay series, and for himself. We Think.
Darkstalkers: Morrigan and Lilith are technically two fragments of the same soul. The game art depicts them embracing, naked. What did you expect from Horny Devils? Also, it's not just the game art. In Darkstalkers/Red Earth: Maleficarum is a 2-page picture with Lilith once again embracing Morrigan while looking back at the reader with a knowing grin. (But they're wearing their scanty costumes this time.)
In Final Fantasy VII, Cloud can visit a brothel. In one of the rooms he has one of his frequent psychotic episodes and hallucinates another him, crouched in pain by the hot tub. If you speak to the other Cloud, he berates the real Cloud for being in a place like this, and then leans in to kiss Cloud. The real Cloud passes out as their lips touch.
And the Genesis Copies in Crisis Core. And if Angeal wasn't dead by the time, he and Lazard would have been candidates.
Breeding with Ditto in the Pokemon games may invoke this trope. (We don't know for sure because, if anyone's actually seen the Hot Skitty-on-Wailord Action in person, they aren't admitting it to the protagonists.)
In Digital Devil Saga it is almost casually mentioned how Sera was conceived of Jenna Angel's egg AND sperm. This is supposedly possible because she is a Hermaphrodite.
Adding onto the Atlus, Raidou'sseries have a dimensional rift, allowing Raidou to meet another version of himself: Raido Kuzunoha XIV — whose differences include scars on his face and speaking like a normal character. While they don't stay together all that long (because their meetings always end in one sending the other back to his original dimension) fanon sometimes persists in shipping the two, mainly played for drama.
Played with in Kingdom Hearts 358 Days Over 2. Roxas and Xion become quite close, and Xigbar even gives Roxas dating advice to impress Xion. This quickly turns disturbing when it is revealed Xion is a Sora clone. Oh, and she's been sucking the life out of Roxas the whole time, and she doesn't even know it. It gets even more ridiculous when you learn that Xigbar at some point sees Xion as Ventus of Birth by Sleep — and while not the same person as Roxas the two do look suspiciously alike.
In Sam and Max Season 2 Episode 1, ghosts of Sam and Max travel to the Christmas of the Future to save their future selves from dying a horrible death on a river of lava. If Sam suggests haunting their future selves, Max says that they should, only if he haunts Future Sam and Sam haunts Future Max — "otherwise, it'd just be gross". However, he also hits on his future self — "Hey, sexy! I'll be back to pick you up later!"
Modifying the visuals of certain games, such as Resident Evil, can allow this sort of thing to occur. For example, this video replacing both The Vamp Excella trying to flirt with Big Bad Wesker in 5 with Chris (although despite the change in appearance the mechanics for the original characters still operate, such as Excella's Jiggle Physics applying to Chris's chest gear).
In the Old World Blues DLC of Fallout New Vegas, with the right perk you can flirt with your own brain and squick it/yourself out.
Thanks to the Supernatural expansion's Alchemy potions, in The Sims 3 your sim can brew up a clone potion, use it to clone themselves, romance said clone and then, well, this trope.
Bio Shock Infinite: Really not difficult at all what with Tears. In fact, it actually happened. Narcissism, thy name is Rosalind/Robert Lutece.
In the Good Ending/True Ending Route of Hyperdimension Neptunia V, Neptune finally gets to see her alternate self, Purple Heart via Cloning Blues (long story), and thinks that she's a cool, beautiful, and stylish woman. Sparkly eyes included.
The eroge X-Change toyed with the idea, having one of the girls apparently resemble Takuya's female form, but with a different hair color.
This BL Game features uke salesman, Saeki Katsuya, who turns into a super sadistic seme when he puts on a pair of glasses given to him by a mysterious stranger. Several of the game's bonus scenes feature his glasses-wearing seme self doing very naughty things to the normal version.
Played to the hilt in the sequel Kichiku Megane R where two of the bonus scenes revolve around the two Katsuya's getting married.Lampshaded when glasses-wearing Katsuya points out that this is only possible because the sequel is also a fandisc.
In episode 10 of Retarded Animal Babies, the protagonists travel through the internet, find their creator's Newgrounds profile, and end up entering the beginning of the same episode. Effectively, they have traveled a few minutes into the past and are able to communicate with their past selves. The two Puppies immediately decide to have sex.
Well, it doesn't involve time travel but Black Mage of 8-Bit Theater has an Enemy Without moment, but ends up killing the embodiment of his sins (himself) and re-absorbing all of his evil. Then he decides he needs to do something that makes self-love into an atrocity. Thief then somehow gets pictures and blackmails him.
Karkat has wondered whether he could be his own kismesis, although in practice that doesn't really work, even considering troll biology. In fact, this seems to be something of a recurring theme with him — when he sees Jade arguing with her Dreamsprite, he fantasizes about them making out and accidentally mistypes "make myself out to be" as "make out with myself to be" in the connecting log with her.
This update reveals that one of Nepeta'smany, many ships is Jade auspisticing between past Karkat and future Karkat. Definitely a recurring theme. note Although because of how incredibly weird Troll Reproduction is, it isn't entirely clear if Auspisticing would count, considering it lies in what is, for lack of a better term, the platonic half of troll relationships.
Subverted in a strip: Greg and Tony travel to an alternate dimension where everyone is gender-flipped. Upon meeting female Greg, Tony comments that female Greg is kinda hot. Greg's reaction to this is not surprising in the least.
Wicked Powered has this as the origin of the main character. Due to a complex sequence of Time Travel, genderbending, and amnesia, he became both of his own parents. And this made him immortal. Oh. And his "aunt" is actually his pet monkey.
Touched on in A Softer World. "I would totally make out with my clone. If it was okay with her. No pressure."
Erin from Dragon City has admitted to being attracted to an alternate universe version of herself, but her dad pointed out that she might just be narcissistic.
When he first gets turned into a woman, after a night of drinking Tiffany of Exiern remarks that she's not as turned on looking at her new body as she thought she would be. Followed by a moment of Brain Bleach at the thought of checking herself out.
In one strip of The Non-Adventures of Wonderella, the main character is split into two individuals, each representing a part of her personality. One Wonderella asks whether they have to have sex with each other to fix the problem. The other Wonderella says she’s straight but is willing to "lay back". Doctor Shark eventually solves the problem without any intercourse.
In the Whateley Universe, this is a serious problem to Jobe, as his now-identical clone Belephoebe is also in the body of his ideal girlfriend. And is his daughter, legally. He restrains himself from the urge to make sweet monkey love to her. Even after Jobe is turned into a girl. Belephoebe, however, does NOT restrain herself.
Cracked also ran a video in which Swaim speculates about having sex with his own clone. He decides that the morning after would be akward.
Clone #1: What do you want to do? Clone #2: I... want to die.
And then Agents of Cracked had an episode featuring a Similar Squad, with Dan O'Brien's doppleganger invoking the article written by his counterpart.
Brian O'Donovan: You know, I remember reading somewhere that there are only two truly meaningful things you can do with your doppleganger when you're locked in a room. You can fight them... Or f#@k them. (Dan takes a fighting stance) Brian: Wrong answer.
A later episode has Swaim reference this incident, and then provide many potential alternate names for this trope.
Swaim: You slept with your exact duplicate. The clone bone. Sixty-sixing. Dopplegangbang. Mirrorbation. The big auto-erotic enchilada. Twins with benefits.
In the Funny or Die video "Go Fuck Yourself with Dave Franco", the titular Franco goes to a bar, hooks up with himself, and eventually fucks himself. The link is slightly NSFW.
House Stevens is made up of clones who only have sex with those they share their genotype with. This was originally to prevent inbreeding as the 47 original founders were the only humans on their planet and they were all related, so basically incest is okay as long as it's with yourself.
Also implied to be happening at the end of Betrayals between Gus and a copy who had been living in a virch for years.
In the Global Guardians PBEM Universe, a muckraking tabloid once accused superher Los Hermanos of having done this. While he denied he ever had done so (or even having ever thought about doing so), he also shocked his teammates by admitted that the idea wasn't as repugant to him as they thought it should be as, given that he and his duplicates are a Hive Mind, it would be more akin to masturbation than anything else.
Lampshaded in MEL when the eponymous protagonist ends up with not only his love interest but an older version of her from a future where she was embittered by HIS death.
"He was fiercely aroused all of a sudden, and he realized that his situation was somewhere in between The Graduate and the lucky guy who gets to take home those blonde beer-ad twins — no incest taboo, just something more sublime and disturbing. He didn't want to think about it too earnestly, for fear of blowing up the universe."
It doesn't last however, as the two versions leave him for each other.
Rhett & Linkhavethis video about choosing the perfect profile picture. After taking the appropriate steps and multiple shots, "pick the one picture in which you are most physically attracted to yourself".
A sketch on Robot Chicken parodying Best Week Ever, featured Hal Sparks (portrayed as pretty much all people on that show are, as a stop motion action figure) remarking "If anyone ever made a toy of me, I'd have to make out with it". A few seconds later, Hal is shown making out with a considerably less animate but otherwise identical copy of himself. A moment after THAT, he pauses to cheerfully declare to the camera, "It's not gay, it's masturbation!"
It's nowhere near sex, but Fry does say Lars has a "ruggedly good looking face," before he learns Lars' true identity.
This is of course the very first thing a nudist alien does after thinking he finds the secret to paradox-free Time Travel in Bender's Big Score.
In one of its countless Imagine Spots, The Simpsons had Homer fantasizing what it'd be like to marry himself. Cue the image of a room full of mini-Homers and two adult Homers swapping tongue.
Arguably, Warden paired with either himself or his future self is one of the more popular pairings in the Superjail fandom, fueled by a scene in which two versions of himself hug each other at their trial, prompting the judge to tell him to "stop touching yourself!"
An episode of Family Guy features Stewie and Brian travelling to other universes, one being where everyone has two heads: One happy, one sad. When we see this universe's Stewie, we see his heads kissing each other. The happy one likes it, while the sad one tries his best to.
Aeon Flux has an episode where Aeon is duplicated and, true to her omnisexual nature, makes out with herself, though only briefly... on camera. There was more than one duplicate. And they were all naked, in the same room. Yes, the Big Bad had a cloned harem of his primary nemesis.
An episode of American Dad has a future version of Stan offering the Stan from the present a "handy J." According to future Stan, it's not gay, it's "you on you."
On Young Justice, Miss Martian demonstrates her shapeshifting powers by turning into female versions of Robin and Kid Flash, leading Kid Flash to wonder, "Is it wrong that I think I'm hot?"
Ron Howard (and Tom Hanks, but only incidentally) was so narcisistic that he forced hookers to wear mirrors on their faces. Eventually, that wasn't enough for him, so he wanted Frankenstein to make a clone of him. He agreed, but Ron felt it was taking too long and started jumping back through time to have sex with younger versions of himself. This ultimately collapsed the timeline and resulted in a universe populated by an infinite number of Ron Howards.
Also with the Were-Lawrence. He finally finds a woman who loves him. Only, having bitten her, she turns into his human form whenever sexually aroused.
In the episode "Johnny Alternative", it's strongly implied that Johnny Test falls in love with a female version of himself.
A PG version in the episode "A Glitch Is A Glitch" of Adventure Time, in which the Ice King is convinced that Princess Bubblegum will go out with him if he was the last person in Ooo. His evil scheme of the episode does indeed remove everyone from Ooo, but when he comes to collect, Princess Bubblegum realizes that there is one person in Ooo other than the Ice King - herself. She proceeds to spend most the episode's remaining run time making out with her own hand.