An episode of The Adventures of Brisco County, Jr. has Brisco defending his friend from a murder charge, which gets pretty tricky when it turns out his friend was having an affair with the victim's wife. It turns out the victim's secretary was obviously in love with the friend, and when he turned her down in favor of the affair, she conspired with her boss, who had a terminal disease, to frame him for the man's murder. Once the whole scheme is revealed, she tries to shoot him in the middle of the courtroom.
The Blacklist: In the episode "Lady Ambrosia", Tom's ex-girlfriend kisses him and asks him to come with her Tom politely turns her down, because he already has someone (Liz) and he wants to get back to her. She looks upset at this and later gives him one more chance to come with her. Again, he refuses. Without missing a beat, his ex jumps out of the van and gets her men to shoot everybody in the van. Basically, she has not only Tom but her entire team murdered as well. She then tells someone to set fire to the van with the bodies inside.
On Big Love, Rhonda, the child bride of the cult leader, trades shamelessly on her status as an abuse victim, right up to the point when she flips completely and flaunts her status as bride of the Prophet. She's willing to blackmail and manipulate, but she takes pains to appear as a sweet innocent to anyone she's not specifically attacking. Later on, she escapes from the compound and is able to adopt fame as being an escapee from a fundamentalist compound. Sarah tries to tell Rhonda's community worker about Rhonda's dark side tendencies and is shocked to discover that the worker is well aware of them. She justifies them on the grounds that Rhonda grew up on, well, a polygamist compound and adapted them as a survival mechanism. Sarah is visibly shaken when she is told that Rhonda's attitude is more deserving of pity than scorn.
A female suspect in Bones was instantly attracted to Booth, claiming that she felt a special connection between them. Despite stalking the victim in the episode, she was not the murderer and seemed harmless. However, when she spotted Booth paying more attention to Brennan than her, she took out a gun to kill Brennan right then and there.
In one episode, Xander used a spell that turned every female in town (except the intended target) into someone who desperately wanted him, to the point where they would cut him to pieces. This included Unlucky Childhood Friend Willow, who at that point was a sweet, somewhat doormat-y personality, but was at the forefront of the 'chop Xander into pieces' crowd.
In another episode, we learn about a student who shot his teacher/lover years earlier when his ghost re-enact their deaths, possessing various students.
In a third, some random student inherits a magic jacket that turns all the women again into love-crazed psychos, including Buffy, Dawn, and Willow (whose plan was to turn him into a girl).
Normal Willow has definite Yandere tendencies. When Oz leaves her because an encounter with another werewolf makes him realise what a danger he could be in the 4th season, she almost performs a spell that would have made both him and the other woman miserable for the rest of their lives (she backs out at the last minute), and later is disappointed that she didn't bewitch him into staying with her. Later, when she and Tara have a fight, Willow wipes her memory, and when Tara is killed Willow flays Warren, her killer, alive, kills another man who had little to do with anything, is determined to kill two people who had little to do with what she wants them dead for, is perfectly willing to kill all her friends for getting in the way, and eventually decides to just kill off the entire world.
Warren, leading him to turn brainwash his ex-girlfriend into a love slave, and accidentally kill her when she broke free.
Anya. In her first human life Anya cursed her cheating husband by turning into a troll (leading her to become a Vengeance Demon in the first place). A thousand years later she tried to curse Xander as soon as became a demon again for leaving her at the altar and made several (unsuccessful) attempts for their friends to "wish" a curse on him.
Buffy's sweet-do-good boyfriend, Riley, went crazy on more than one occasion. He picked a fight with Angel and attacked a harmless chipped Spike by throwing him out into the sunlight and stabbing him with a plastic wood stake when he thought they threatened his relationship with Buffy. He also "cheated" on Buffy by letting a bunch of vampires suck on him to "even the score" after Buffy let Dracula bite her.
After her boyfriend begins to fall for someone else, a woman murders her romantic rival in order for him to forget about her. It sort of works: the two get married, but it's clear that he still has feelings for the rival when her body is discovered years later.
A woman killed her teenage daughter because she thought that her daughter was trying to steal her new boyfriend.
Another woman drowned her daughter because she (wrongly) believed that her boyfriend didn't want to raise a child that wasn't his.
A non-romantic example: a young girl admits to killing her brother's girlfriend, though she later admits to CSI Sara Sidle that she's really covering for her brother. The two show up in a later episode where the girl really does kill a love interest of her brother, in order to frame him and put him in prison where she can always keep an eye on him; though he ends up killing himself in his jail cell, much to her dismay. The whole ordeal pushes the already stressed Sidle into (temporarily) quitting the CSIs.
One particularly disturbing example has a teenage-ish girl who is this towards her father, a lesser degree.
Ella McBride was portrayed as one of these for Mac Taylor. She followed him to the grocery store, gave him fake evidence so she could "help" with the case. She even slit her wrists in an attempt for him to pay attention to her. She also wrote on a card on her wall, "I will make him love me." Nothing came of it except that Mac visited her in a group home and she said something about an eyeball dropping into coffee which happened to Stella earlier in the episode while she was with Mac.
Another episode centered around a man with two wives who was murdered. And the end of the episode it's revealed that his first wife killed him, because she was jealous of the attention that he was giving to the second wife during sex. When asked why she didn't just get a divorce, the woman says that it was because she loved her husband too much.
Stella's ex-boyfriend holds her hostage and tries to kill her after she breaks it off with him.
Iris Crowe from Carnivàle; okay, so maybe it doesn't take much to figure out that her brother isn't going to be Mr. Nice Minister forever, but surely she's just a sweet, devoted church lady? Okay, maybe a little too devoted, but... still pretty harmless, yeah? I mean, right up until she's burning down a church full of orphans to throw suspicion on the city councilors who wanted to shut down her brother's ministry.
Cole evolved into this in his last days. In season 5 he returned and Phoebe wanted nothing more to do with him. He gradually went mad and was desperate to get her back. He even had her mummified and rewrote time so that they'd still be together. Though given the poor way the writers handled this, corresponding with Phoebe becoming a Designated Hero, a lot of fans were Rooting for the Empire.
In the Cheers episode "A Ditch in Time", Sam Malone gets involved with Amanda Boyer, who becomes obsessed with and possessive of men she goes out with. When he tries to break up with her she implies that she'll commit suicide if he does.
The most prominent would be Maya Sharma. When in a relationship with Dev, she slowly started demonstrating hints of craziness such as kidnapping Tyrone's dog, tricking Dev into leaving a restaurant without paying and driving at a dangerous speed until he proposed to her. When he dumped her for Sunita, she first trashed his flat. Then she manipulated one of his ex-employees into suing him for sexual harassment. Then she went really crazy and married six illegal immigrants in Sunita's name and thus she was arrested on her wedding day to Dev and sent to prison for weeks. Maya eventually was found out but she pulled off one last elaborate Yandere scheme - rigging all of Dev's shops with explosives and setting fire to the last with him and Sunita tied up inside. All because Dev had left her for Sunita.
Karen McDonald was increasingly possessive of her husband Steve, especially when she found out he was the father of Tracy's baby. Yes you read that right, Karen was the evil Rival to Tracy Barlow. She refused to allow Steve to see his daughter and he frequently had to hide things from her, afraid of how she would react. After she suffered a miscarriage, she went completely off the rails. She kidnapped Steve and Tracy's daughter and set fire to the car, though it was later revealed she had left the baby with someone else.
Tracy herself demonstrated some Yandere tendencies towards Steve after the relationship with Karen folded. She even tried to set him up of kidnapping their daughter and trying to take her out of the country. After she got out of prison her Yandere tendencies have vanished. She's still crazy but seems to be doing it more For the Evulz than out of 'love' for Steve.
Lucy, Peter Barlow's first wife. He married her while he was engaged to Shelly and she immediately threw him out. When she discovered he and Shelly had married, she told Shelly and attempted to have Peter arrested. When he wasn't, she was still determined to mess up his life and any chance he and Shelly had to reconcile. She invited Peter over and phoned Shelly to try and fool her into thinking Peter was sleeping with her [Lucy] again. After a while she gave Peter an ultimatum - move to Spain with her and their son or stay in Manchester with Shelly. When he told Shelly he was planning to move for the sake of their son, Lucy revealed she hadn't bought Peter a plane ticket and had set the whole thing up. When he confronted her at the airport, he discovered she had lied again and was going to Australia instead of Spain. Laser-Guided Karma caught up with her six years later and she died of cancer offscreen.
Kirstie Soames, Tyrone Dobb's physically and mentally abusive partner, is extremely possessive of Tyrone and fiercely jealous of his late wife Molly and his ex-girlfriend Fiz, frequently snapping at Tyrone for even talking with the latter. She gets worse as she becomes more violent with him, going so far as to threaten Fiz and rig a workplace accident so that Fiz ends up sewing her finger while trying to fix the sewing machine. Later, Kirstie traps Tyrone in a relationship with her by leaving his name off of their newborn baby's birth certificate so that he can't take the baby and leave her when he finally has enough of her abuse.
Played with in a few ways with Rebecca Bunch in Crazy Ex-Girlfriend. Throughout the first two seasons, she shows obsessive tendencies in her love life that arent violent, but definitely invasive and manipulative. Then the season two finale sheds a darker light on this: a previous affair she had with a professor who refused to leave his wife ended with her burning down his apartment, which got her committed to a mental hospital. This comes to light as Josh leaves her at the altar and she declares that he must be destroyed, but the next season shows that she ultimately cant go through with it. Eventually, she comes to recognize the patternand decides not to pursue another relationship until she has a better handle on her issues.
Dark Shadows: Angelique's obsessive attraction to Barnabas Collins lay at the back of much of the bloodshed and madness that haunted the Collins clan for 200 years, and since she was a very powerful witch, she had the power to back up her obsessions. In one of the classic scenes from the show, she tells Barnabas (in a very kind, gentle, loving way), that she loves him so much that she would kill anyone to possess him. The look on Barnabas's face is classic, as he is reminded once more that she is bonkers nuts.
Degrassi High gave us Claude. Caitlin left Joey for Claude, who was an activist like her. They spray-painted antinuclear slogans on a nuclear power plant, the cops caught them, and Claude left her there. She dumped him on the spot. The next year, he recited a poem about death, shot himself in the bathroom, and sent her some flowers and a note saying he forgave her.
Orson's ex-wife who was believed to be dead in season 3. Her story arc first makes her out to be the victim of the situation before it is revealed that she disappeared and re-appeared for the sole purpose of getting revenge on Orson for not returning her love... by drugging him up and raping him. Because she wants to have his baby.
George, a pharmacist, lusted after Bree once she ended their affair together and became jealous of her husband Rex. So he tampered with Rex's prescription drugs by replacing his heart medication with placebos. He also beats up and attempts to kill other people who look like they are trying to come in between him and Bree. He also drugged Bree at one point and was seriously considering taking advantage of her. He eventually proposed to Bree and pressured her into marrying him. After the engagement he became increasingly possessive of her, and increasingly violent.
As of the 9th episode of season 6, Katherine has officially gone over into this. She started out jumping back and forth between being a Woman Scorned resorting to usual desperate housewives antics, and a Stalker with a Crush resorting to tactics that suggested signs of instability (like scratching up Bree's car) before finally begging Mike to kill her, then stabbing herself. She got better. Turns out she's much more sane in a lesbian relationship.
Dexter: Lila has Dexter ambushed in a parking lot by a man who wanted to kill him because she thought it would bring them closer. When Dexter dumped her, she obsessively tried to win him back with methods including arson and framing one of his friends for sexual assault. She also burned down her ex-boyfriend's house with him still inside. Said arson methods weren't just used on Dexter - she put Rita's kids, essentially her competition, in serious danger as well. She makes Dexter, a sociopathicSerial Killer, look sane by comparison.
In Doctor Who, we have Missy, who gleefully self-describes as "bananas." She also does her best to kill any woman who shows any form of interest in the Doctor, even platonically. At first, it's not clear where she met the Doctor, even though she refers to him as her "boyfriend", but everything falls into place when it's revealed she's a female incarnation of the Master.
Missy: Oh, 'Clara, Clara, Clara'! You know, I should shoot you in a jealous rage. Now wouldn't that be sexy?
Family Matters: Myra secretly put a camera in Steve's glasses so she can see what he's doing at all times.
In Frasier, Niles's wife Maris reveals herself as one of these in addition to everythingelse. During the couple's divorce proceedings, she has second thoughts and plies Niles with gifts and love letters asking him to reconcile. Niles rejects her, citing the fact that after she has manipulated him, cheated on him, and treated him like dirt under her feet for years, she had some gall to ask him to come back to her. She goes into a Tranquil Fury and then proceeds to unleash a team of lawyers upon Niles to screw him out of every cent he has by any means necessary, legal or not, notifying him with a Valentine reading "Roses are Red / Violets are fickle / When I'm done with you / All you'll have left is this nickel."
Lysa Arryn has loved Petyr Baelish her whole life and has always been jealous that he loved her sister more. Even after Lysa and Petyr get married, Lysa gets more than a little crazed at the thought of Petyr being involved with someone else, to the point that she physically injures her own niece, who is fifteen years old and has no interest in Petyr at all.
Petyr Baelish to Catelyn Stark. He helps get her husband killed and starts a war partially to get her, despite her complete lack of interest in him. He then moves onto her daughter, when he can't have her.
Ramsay's paramour Myranda is a petite and cute looking girl who appears to be sweetness and light at first, but is actually dangerously obsessed with Ramsay and willing to kill anyone she sees as a rival to his affection. For example, when he described another girl as pretty, she had the girl hunted down with dogs, remarking "Not so pretty anymore", as the girl was mauled to death.
The Goldbergs has Beverly Goldberg, who is a very loving mother...too loving. As described by Adam, his own mom goes beyond the boundaries of a good mother. So much so that upsetting her is a risky move, by both relative and stranger alike.
Barbara alternates between pining over Jim and wanting to hurt him for him choosing Leslie over her.
Edward Nygma (The Riddler) develops Sanity Slippage and a split personality disorder partially because Ms. Kringle didn't return his affections and killed her boyfriend when he found out how he treated her. He ends up accidentally killing her while telling her that he killed her boyfriend "for" her.
In season 2 of Hannibal, Hannibal Lecter serves as this to Will Graham. After framing Will for his murders, Hannibal continues to visit Will at the psychiatric institution and involve himself in Will's trial. He's clearly obsessed with Will, talking about him endlessly with Jack, Bedelia, and Chilton. "Hassun" implies that his killings and machinations are depraved attempts to express love for Will. His love for Will only deepens in season 3, which worsens his more spiteful, possessive tendencies. He leaves a "valentine from a broken man" for Will in the form of a corpse wrapped into a heart, takes Will captive in Italy and attempts to cut open his skull to eat his brain, and saves him from Mason's wrath (carrying him in almost the exact way another Hannibal Lecter did his love interest). Hannibal then proceeds to give himself up to the FBI, potentially being put away for life, just so that he can get back at Will for rejecting him. He also attempts having Will's wife and step-son killed by another killer, just to get Will's attention.
Harper's Island: Henry marries someone just to get his half-sister onto the island, conspires with his real father (John Wakefield) to kill everyone apart from Abby, kills him so Abby can live, and makes it seem as if she and him died so he can start over. This is all because when they were elementary school-age, Abby said that she wanted it just to be the two of them.
Sienna Blake is a repeat offender. She faked a pregnancy to get Darren Osborne to stay with her, and when that didn't work, she had his wife institutionalised and tried to kill his children. She later became obsessed with her own twin brother and imprisoned him in a basement over Christmas, trying to force him to "marry" her.
One of the Hollyoaks Later specials featured a girl called Jade, who befriends (and seduces) Esther and Tilly during a holiday. It turns out Jade's boyfriend had been the donor of the transplanted liver Esther received, so Jade planned to kill Esther and cut out the liver in a bizarre attempt to bring her boyfriend back to life.
Kim Butterfield stalks Grace Black, makes many attempts to destroy Grace's relationship with Trevor, and even gets herself sent to jail while Grace is there so that they can be together. It's also discovered that Kim previously stalked her sister's ex-fiancé.
One episode of Honey, I Shrunk the Kids had Wayne build a security system named F.R.A.N. after a burglary occurred in the house. F.R.A.N. develops a crush on her inventor and got jealous of Diane. However, once Wayne seemingly de-programmed F.R.A.N., the system decides to kill him, deeming him as a threat.
Spencer goes out with Carly's teacher Mrs. Ackerman, who seems perfect for him, but later turns out to be extremely mentally unstable.
Lewbert is revealed to have a Psycho Ex-Girlfriend named Marta in "iFind Lewbert's Lost Love". After the first two weeks of their relationship, she became possessive and controlling of him. The stress of the relationship became too much for him that he tried running away from her. Years after living of living in a new place far away from her, he "reunited" with her, which understandably caused him to freak out and demand her to leave. She picked up right where they left off and she resumed her role as a Control Freak. Even when the iCarly team tried to help Lewbert get away from her, Marta accused Carly of trying to get Lewbert all to herself. Of course Carly points out how ridiculous that sounds, especially since she's fifteen and Lewbert's in his thirties.
Nora initially seems like a socially awkward girl who really wants some friends, but Carly and her friends learn the truth about her: she's mentally unstable and is determined, by any means necessary, to keep her new "friends" from leaving her. In iStill Psycho, she returns and is willing to repeat the same events from iPsycho, this time with her parents helping her.
Jessica Jones (2015): Prior to the series, Kilgrave became obsessed with Jessica when she managed to escape his mind control after he made her kill Luke Cage's wife. He spends much of the series stalking her and committing various atrocities in attempting to "win her back", i.e. Mind Rape her again.
On Jessie, Creepy Connie is this towards Luke starting in "Creepy Connie Comes A Callin'." In her 2nd time in the show (Creepy Connie's Curtain Call), she went apeshit over Luke in the play just so she can kiss him. On her 3rd time? (Creepy Connie 3: The Creepening) She brings out a whole wedding for her and Luke (Luke of course, gets bound in a wheelbarrow lift on a rope), with those who tried to stop her also bound to their chairs TO WITNESS THEIR WEDDING!
Masato Kusaka in Kamen Rider Faiz is a rare male example of this. He replaces the "cute, delicate, and sweet" facade with one that is strong, supremely competent and handsome, but his inner obsession with Mari fits this exactly. Taken to the extreme in the non-canon novel where he goes as far as to rape her.
In Kamen Rider Fourze, Makise/Pyxis Zodiarts tried to use his powers to force girls to be with him, eventually trying to send several girls plummeting off a cliff to their deaths because they rejected him.
Jiro in Kamen Rider Kiva is obsessed with Yuri, whom he sees as his only hope of reviving the Wolfen race. He tries to kill Otoya as a rival for Yuri; then tries to kill Yuri too because she refuses to marry him.
After being rewired in Season 3, 790 transferred his affection from Xev to Kai. At first he was just a little snippy and jealous. In Season 4 he went completely over the top, so desperate to make Kai love him back that he pulled any number of cruel and psychotic tricks, including sending Stan and Xev to a secluded island where he knew they would be horribly killed in order to eliminate any possible competition and having his head grafted onto a body onto which an enormous penis had also been grafted and then forcing himself into Kai's personal space in a rather creepy way.
He acted much the same to Zev/Xev. It's just that, unlike Xev, Kai is dead and instead of actively holding back 790's darker it was left unchecked as the deadcan only react to what has happened and tend to ignore the little things that would have kept 790 from getting so desperate. Even when still obsessed with Zev 790 tried repeatedly to get Stan killed or maimed, though he tended to ignore Kai as Kai had no interest in Zev.
The episode "Bedtime" from Law & Order: SVU featured a female police officer who fell in love with a mattress salesman. When he didn't leave his wife quickly enough, she killed her, convinced him that he was going down for the murder, then faked his death and kept him trapped in her apartment for 35 years.
The episode "Conned" featured a female Psycho Psychologist who fell in love with a teenage client and sexually took advantage of him. When she eventually became pregnant she tried to manipulate him into staying with her by using his abandonment issues against him. When he finally tried to leave her for a girl his own age she called her parents saying he was a rapist, then intentionally misdiagnosed him with schizophrenia so she could keep him drugged up in an institution. When he escaped, she pretended to work with detectives to "rescue" him so she could get him back.
Ben from Lost has a serious case of this towards Juliet. He summed it up pretty nicely in this dialogue from one of Juliet's flashbacks, when Ben's orders ended up in her lover's death:
Juliet: You wanted this. You wanted him to die! ... Why?
Ben:(incredulous) Why? You're asking me... (gets closer to her) why?! After everything I did to get you here, after everything I did to keep you here, how could you possibly not understand... (Beat) that you're mine.
Fanny de Praslin, as she is portrayed in La Caméra explore le temps is this for her aloof husband Charles. However, her violence is only verbal (with threats of suicide here and there), and in the end, it is Charles who snaps and kills her.
The episode "Faetal Attraction" from Lost Girl has two: A fury suspects her husband is seeing someone else (outside of the threesomes they have to "spice up" their love life) and, after failing to convice Bo to Murder the Hypotenuse, tries to do the deed herself. Then, when her husband is found without his head, everyone assumes she was the killer. Except it turns out that the girl she was trying to kill was stalking her husband and ultimately killed him and took his head for the collection of her previous "lovers." And now said-girl has her eyes on Bo and is planning a double-suicide for her...
A somewhat unconventional example, but Old Gregg from The Mighty Boosh is yandere for Howard Moon, alternately courting and threatening him constantly and within minutes of meeting him for the first time.
Old Gregg: I'm gonna hurt you. Howard Moon: What? Old Gregg: I like you. What do you think of me?
Fernando Vera in Mr. Robot was at first obsessed with his drug dealer Shayla to the point that he didn't want anyone else to come near her, even Elliot. Later, he gets over her and executes her after he ends up turning his obsession to Elliot when he finds out that his hacking skills got him arrested in the first place. He tells him in an unsettling manner that he loves his power and wants it so bad. He ends up coming back to Elliot's apartment complex at the end of Season 3 and in Season 4 desires to make him his partner so that he could be the king of New York. He even goes as far as to kidnapping Elliot's therapist Krista to get more information about how he could break Elliot so that he could have him all to himself and control him. He then finally kidnaps Elliot and threatens to rape or kill Krista if he doesn't become his partner/architect. He finally drives Elliot insane by forcing him into a therapy session where he finds out that he was molested by his father, leaving him devastated. He successfully manipulates him into believing he is his only savior, that is until Krista kills him.
Miss Piggy from The Muppet Show is an obvious one. Rather animesque in that, though she often randomly attacks everyone over any minor thing, the one who she is really most likely to Falcon Punch across the room is her "Kermie".
In "The Sins of Castle Cove," Elis the bookkeeper was obsessed with Miriam, the murder victim. He believed that she had feelings for him even though she was married and was clearly not interested in him at all. When he read the titular book and found the section that revealed her true feelings for him, he confronted her, hoping that he was mistaken. Unable to cope with the bitter reality, he struck her down out of anger. When he's revealed as the murderer, he even says, "She should have loved me! I loved her so much!"
Male example in the episode "Love & War": the murder of the week turns out to have been arranged by the ex-fiancé of the victim's daughter. She had resumed their relationship after her mother died of cancer, so after she broke up with him a second time, he arranged her father's death in the hopes that the hurt/comfort scenario would repeat itself.
In "Terminal Leave", a female officer is apparently being targeted by terrorists. The would-be killer turns out to be the neighbor with whom her husband had an affair while she was deployed.
In the episode "Thirst" Ducky's girlfriend, Mary, proves to be the killer of two service men all to show Ducky how much she loves him.
Zelena toward Rumplestilskin. She locked in first in a cage in his own home and then in a cage in her basement while she had control over him with his dagger. During that time, she also forced him on a date. She only had his dagger because she brought him back from the dead by tricking his son Neal into sacrificing himself.
Regina was a platonic example towards Henry. She instantly tries intimidating Henry's actual mother when she meets her.
Chris Keller in Oz over Beecher. He kills every guy that Beecher sleeps with and the guy who murdered Beecher's father, has Beecher murder Schillinger unknowingly, acts overly aggressive with him at times, on two occasions has knocked him out with a blow to the head when Beecher goes against his wishes and later handcuffs him to a chair away from other people where he forces a kiss on him, and finally murders the Aryans so that they don't pose a threat to him or Beecher anymore.
As well as Ryan over Dr. Nathan. After she helped him through cancer, he immediately divorces his wife. Later, he forced a kiss on her, paid a fellow inmate to steal her stethoscope, and when she started ignoring him, had his brother Cyril kill her husband. After she was raped, he very quickly murdered the man that did it. It was even said outright that his love for her was more of an unhealthy obsession. However, Dr. Nathan actually falls for him in the end.
Divatox is one towards Malagor as she tried to sacrifice Kimberly, the original Pink Ranger, and Jason, the original red/gold Zeo Ranger. After Malagor was destroyed, she swore revenge on the Power Rangers.
Many characters from Argentine soap Padre Coraje, but mainly Norita (who murdered two people, tried to tried to kill her sister at least once a month, and stole her ex-not really husband's body), and Ana (who tried to kill her sister several times, along with many other schemes).
Person of Interest: Root, who is obsessed with The Machine as well as to its creator Harold Finch. When she gets into a quasi-relationship with Shaw, she also shows this tendency as well, casually threatening the life of the man Shaw is on a not quite date with.
Perry Mason gives a male example. A seemingly charming and likable man ends up trying to blackmail the girl, and says as his reason for doing so, "Because I want you, and if I can't have you, no one else will."
The supernatural mini-series Remember Me has Isha, Tom Parfitt's Indian ayah who had drowned when he was a child. Her ghost still saw the now elderly Tom as her charge and began obsessively killing anyone who she saw as taking over her role as his caretaker. The reason she came back from the dead? Tom was getting cold feet about marriage and accidentally summoned her. He accidentally pushes his wife to her death and Isha has haunted him ever since until she follows him to a lake where he ultimately drowns himself.
Rescue Me has Sheila Keefe. It gets especially bad in season 3, when she drugs Tommy and rapes him in his sleep, then smashes up his kitchen after finding out he went on a date with his brother's ex. Then she puts alcohol on his lips and lets him believe he fell Off the Wagon and did the damage himself. Then she does it AGAIN in a later episode, this time accidentally setting the house on fire in her rampage and nearly killing them both. She gets away with it both times.
Fauxmanda is this in regards to both Emily and Jack, killing and attempting to kill for both of them in order to keep them in her life.
Natalie, Conrad's ex-mistress, has major streaks of this towards Conrad. She goes as far as to marry Conrad's father and starve him to death in order gain access to the Grayson name and fortune, enters Victoria's social circle in order to undermine Conrad's ex-wife, and attempts to frame David for domestic abuse as a way of posthumously avenging Conrad. As the cherry on top, she erratically declares Lydia- Conrad's other mistress- a "vile whore".
Louise is a classic example, stalking Daniel, attempting to get pregnant by him and locking his girlfriend Margaux in a sauna.
Rigmor from Riget. She's thoroughly obsessed with Dr. Helmer, but as soon as she thinks he's cheating on her, she tries to kill him.
Effy's psychiatrist in Skins, Series 4. Attempts to kill both her love interests. Succeeds with one of them.
Smallville: Alicia Baker has an expressive face with kind eyes and a bright smile. In the beginning of the episode, she uses her power to protect Clark's secret, but by the end, she tried to stab Lana to death for her past with Clark.
Smart Guy did an interesting take on this trope: In order to win over another girl, Marcus, with the help of his brother TJ, hacks into the girl's on-line diary in order to find out what she sees in a guy so he can become her ideal boyfriend. It backfires when he later on reads her diary entries and learns that she has become obsessed over him to the point where she wants to quit school and start a family with him. When he tries to break it off and flirts with another girl, she attempts to run over said girl, culminating in pig masks, axes, and a chase around the house. The twist? She and her friends, including Marcus' sister, Yvette, found out his ruse and planted fake diary entries just to teach him a lesson. Though you have to wonder how much of an inversion it is for someone to think acting like an Ax-Crazy to "teach someone a lesson" is funny....
In Sons of Anarchy ATF Agent Joshua Kohn follows Dr. Tara from Chicago to Charming and engages in increasingly disturbing Stalker with a Crush behavior culminating in an attempted rape/abduction that ends with his death.
Reese in the episode "Menace" seems like a sweet, friendly (if a little spoiled) Robot Girl, but when things don't go her way with Daniel, she creates an army of Replicators which proceed to nearly wipe out the SGC.
Lucifer was kicked out of Heaven for "loving God too much". After the breaking of the 66 Seals, he has returned to Earth to seek revenge. So far, he has focused on murdering the hypotenuse, and by "the hypotenuse" he means "the human race". The first part of this is consistent with some Islamic mystical traditions. When God returns in Season 11, Lucifer is significantly less murderous, they hash out their issues and reconcile, and Lucifer even tries to protect his father, only to wind up abandoned again when God leaves with his sister the Darkness - herself a Yandere for Dean as a Replacement Goldfish for her brother - after her HeelFace Turn. In Season 12, Lucifer hits Despair Event Horizon believing that God only used him to defeat the Darkness, and decides to cause as much destruction as he can as the only means of revenge he has.
Jeffrey in "Repo Man" turns out to be an example... twistedly enough, for the demon that possessed him. He is grateful to the demon for forcing him to enact his violent Serial Killer thoughts and fantasies, and calls him the love of his life, with the reveal that the events of the episode had been plotted by Jeffrey to summon the exorcised demon back from Hell with the ultimate goal of being re-possessed by him. They both end up in Hell by the end, which in all honesty is probably something Jeffrey would be happy with anyway.
An episode of Tales from the Crypt had a couple getting married and sharing a perfect night of passion. Immediately afterward, the woman murders the man to make sure time doesn't spoil their love.
Caroline, one of Fez's girlfriends in That '70s Show. Then subverted when Donna finally just snaps and tells her Fez doesn't love her. A little heartbroken, she asks Fez, who nervously and hesitantly admits. It is, in fact, strongly implied that she had completely snapped from the event, and directly stated that she had spent most of the intervening time on psych drugs and intensive therapy.
The Walking Dead has Shane. When Rick does find his family, Shane slowly goes insane, and convinces himself that Rick isn't fit for being a good enough husband or father to them, and that he's just 'getting in the way'. He even goes so Ax-Crazy to the point of trying to murder him.
Wizards of Waverly Place did this with Harper, towards Justin. Thankfully, she lost this trait before her interest in Zeke. And he conveniently doesn't seem to remember after that, well at least for one time when Harper became Juliet... (Even then, she was done with the behavior, even stating that "Zeke does not need to know this.")
WWE has done this on more than one occasion, including one storyline when Mickie James was introduced as Trish Stratus' biggest fan. Her obsession increased until Trish couldn't take it any more. This resulted in Mickie turning on her beloved.
AJ Lee is the most high-profile recent example of this trope in action in WWE since, as the targets of her... "interest" are the WWE Champion (her most recent crush) and his challenger (her ex).
Protagonist Joe pretends to be a charming Nice Guy towards his target, but is in fact a murderous stalker who wants to "save" his love from anyone who stands in their way. Usually by killing them. As shown in the season one finale, he is even willing to kill his object of affection once they reject him, only to quickly moves into someone else.
The big twist of the second season is that Joe's latest target Love has known about his true nature for a long time and even committed several murders herself to save their relationship. She claims that she doesn't enjoy killing people, but considers it a necessary evil so she and Joe can be happy together.