Semimaru towards Ango in 7 Seeds. He already wasn't absolutely okay with him, but when Ango began helping Natsu, Semimaru really began to hate the guy because Natsu is his.
This has happened to the otherwise pure, sweethearted Belldandy in Ah! My Goddess. During the incident where Keiichi let Shiho stay over at his home to go along with her exorcism hobby, she was a little too affectionate in saying "thank you", and, while trying to suppress her feelings, Belldandy's powers went haywire. Once she realized it, broke down, and finally admitted it, Keiichi told her it was part of being in love... that it wouldn't always be pretty, and forgave her. Keiichi also apologized for taking her feelings for granted and giving her a reason to worry.
First, pre-Eclipse Griffith grows quickly jealous when he notices that Guts and Casca have become an item. It is unclear who he envies more due to his ambiguous sexual orientation. It's possibly both.
Averted with Judeau. Despite his unrequited crush on Casca, he knows he has no chance whatsoever, noticing the bound she and Guts had formed, even before either of them would realize it. Preferring to lose with honour, he helps a lot in the cementing of Guts and Casca's relationship, even going as far as encouraging Guts to take Casca away with him, by force if necessary.
During the Griffith rescue operation, Casca had the Green-Eyed Monster attitude toward Princess Charlotte for a bit, since she admitted that she was still worshiping Griffith like before, even after she and Guts made love for the first time earlier. She tried reconciling to herself, but ended up saying the wrong thing to Guts about the matter, which succeeded in pissing Guts off and awakening the green-eyed monster in him even though HE admitted to himself that he couldn't take his mind off Griffith. But don't worry - they made up later.
Then, post-Eclipse, there's the unspoken rivalry between Sonia and Charlotte. Charlotte is Griffith's Meal Ticket, even though he acts in order to make her feel like he actually values her for herself and NOT her birthright. Sonia is a faithful servant to Griffith, gifted with clairvoyance, and as such considers herself the only girl worthy of him. Sonia is very jealous of Charlotte but her nascent and reciprocated relationship with Irvine might wash it all out.
There's also the jealousy Farnese feels for Casca for being the sole object of Guts's affection. Farnese is technically betrothed to Roderick, who is himself quite handsome, but she definitely has a crush on Guts who doesn't see her beyond being Casca's caretaker. Farnese even breaks down in front of Casca, telling her that she's really ungrateful to ignore Guts after all he did for her but Casca being insane and regressed to infancy, it doesn't really do anything, although Casca seems to understand Farnese's distress. Farnese especially goes through this when fixing Casca's mind, as she witnesses the entirety of Guts and Casca's relationship and becomes very depressed, though she still cared more about reuniting them than her own feelings.
There's also Schierke's Precocious Crush on Guts but, unlike Farnese, Schierke only has shades of this and knows deep down that she's way too young for Guts (he is more than twice her age). Plus, her Puppy Love moments with Isidro also seem to drop some hints about who she may eventually like.
Serpico has a multiple Green Eyed Monster moments towards Guts over his half-sister Farnese since Serpico as her guardian is jealous (even murderously) of Guts giving purpose to her life and Serpico is quick to notice her crush on Guts. However Serpico outright admits this feelings to Guts and thanks him for changing their lives.
Madame Red in Black Butler. The love of her life Earl Phantomhive (Ciel's father) married her beloved sister. She tried to be happy for them but when Ciel was born, jealousy started to consume her. Even when Ciel's parents died in the fire, though devastated, she envied her sister for dying with someone she loves.
In Black★Rock Shooter, Takanashi Yomi becomes a literal Green Eyed Monster when her jealousy over Yuu seeming to take her place as Mato's friend turns her into Dead Master.
Bleach: After Ichigo sinks into depression because his failure to protect resulted in his friends getting badly injured, Orihime can't cheer him but Rukia does by making him resolved to never let any of his True Companions get that injured again. Orihime believes she's incapable of bringing Ichigo out of despair leading her to feel jealous of Rukia's ability which has made her feel useless. This trope is immediately subverted when, instead of becoming bitchy or bitter, Orihime gushes about how wonderful and amazing Rukia is and how bad she feels to be jealous of such a good person. Rangiku resolves the issue almost immediately for her and a few chapters later it's confirmed Rukia and Orihime are very good friends and training hard together.
In the manga of Brigadoon: Marin and Melan, one of the first signs that Melan is developing romantic feelings for Marin is the jealousy or anxiety he displays when he sees her alone (and half-dressed) with another love interest.
Akutagawa Ryunosuke from Bungou Stray Dogs is a human manifestation of this trope. He has displayed hostility to at least two people for getting Dazai's recognition, something he tries hard throughout his life to achieve.
First is Oda, a friend of Dazai used by him to taunt Akutagawa, saying he would never be as strong as the man no matter how hard he tries. After Oda saves Akutagawa, the first thing the boy does is attacking him, thinking he can't be weaker than a mere low-ranking member. He is defeated quickly.
Buso Renkin: Koushaku Chouno's younger brother Jirou deeply resented being born as nothing but a backup heir. Even when his brother was declared unfit and the title of heir was passed to him he still resented that he only got what he wanted because of Koushaku's ailing health rather than merit. When his brother was trying to save his life, and told Jirou that even if he got better he didn't care about the family and wouldn't take back the title of heir it wasn't enough, leading to Jirou trying to destroy the one thing that would save his twin's life.
In Candy Candy, Annie Brighton confesses to Candy White Andree, during an emotional breakdown, that she has always been secretly jealous of her. This is because Annie is Prone to Tears and very scared of reaching out to others, whereas Candy is a fearless Plucky Girl who always reaches to the rest — even in the times when they were heartwarming orphans, Annie always felt less appreciated and loved than Candy was. It's really not helped when the boy that Annie likes, Archie, says that despite caring for Annie, he likes Candy as well. (Partially because he is jealous of her other current love interest, Terry).
Touma's mother looks really scary whenever her husband looks at another woman.
Every member of Touma's harem gets angry when they see him with another girl.
Accelerator and Hamazura's harems get mad when they see the two hang out with Fremea, even though she's only a little girl.
Salia in Cross Ange is this towards Ange, particularly Ange being the pilot of Vilkiss instead of her but this is more because Vilkiss used to be her commander's unit and that she really wants to use it, going as far as switching from her Para-mail to Vilkiss while Ange wasn't around. Her continued lack of attention from their leader Jill leads her down a dark path of oneupsmanship against Ange with her joining the Big Bad Embryo for a good chunk of the second half.
Salia isn't alone in the Ange envy - Julio had her beaten to the punch ages ago. He'd been envious of the preferential treatment her sister received, both from their mother and as the public favorite for empress, so he exposed her as a norma leading to her disgrace and current predicament.
Zenitsu admits that he was more infuriated about the fact Tengen is quite the handsome man and has three beautiful wives than being forced to disguise himself as a female courtesan for their covert demon slaying mission, that however is Played for Laughs and is just one of the many times Zenitsu sees, or simply mistakes, other men having better luck with women than he has.
Daki kidnaps and devours any women who she feels are a threat to her status as the most beautiful oiran in the Yoshiwara Red Light District.
Due to his poor upbringing, Gyutaro is very envious of those he perceives as being more privileged than him. After meeting Tengen, he sarcastically compliments him on his good looks, large physique and popularity with women before declaring that he will give him a tortuous death for being born with everything that he never had as a human.
In Detective Conan Shinichi felt jealous when it seemed any male was interested in Ran, Heiji has been jealous of a magician when Kazuha flirted with him, Kazuha jealous of Ran when she thought Heiji liked her and several other characters showing jealousy.
In D.N.Angel, Riku was jealous that Daisuke seemed to be getting it on with her sister (he wasn't).
Vegeta from Dragon Ball Z has got to be the epitome of this trope. Throughout the entire series Vegeta envies Goku because no matter how hard he trains and fights he is never able to surpass Goku. This becomes a literal case of Green-Eyed Monster when Vegeta becomes a Super Saiyan (the transformation gives you green eyes) and despite finally becoming the warrior of legend that the Saiyan Race had admired for thousands of years in reality, still couldn't let go of his pride. During the era of peace after Goku died he still finds a reason to be jealous because he sees that Goku's family life is more loving and meaningful than his is as Goku's family supported him and made him a better fighter while his didn't show the same results. It is only when Vegeta lets go and admits that becoming better than Goku isn't all there is to his life that he truly shines as a warrior and becomes a good guy.
For a while before Asuka and Shinjigot together, the thought of other women getting near Shinji was enough to get her mad. A while later, when they were already engaged, Mari realized and flirted with Shinji exclusively because she loved messing with Asuka. Needless to say, Asuka was NOT amused.
Saburo was jealous of Rei because Kaworu a long time for her bedside when she fell into a coma. He dumped Kaworu in a fit of jealousy, but when Kaworu and Rei started to hang together his jealousy increased and he started to lash out at Rei.
In The Familiar of Zero both Louise and Saito have shown IMMENSE jealousy whenever the other showed interest in anyone but them (especially Louise).
Also, Momiji points out to Kyo that some other man might marry Tohru if he doesn't overcome his feelings and get her, in order to inspire him. Indeed, when the new school year begins, he overhears some classmates discussing that she's pretty, looks dumb and easy to seduce; this inspires him to walk over to her and look possessive, to drive them off.
A humorous example in the manga (sadly, the scene wasn't in the second anime) is Roy'sreaction when Barry the Chopper grabs Hawkeye around the waist. The fangirls were delighted.
Full Metal Panic!: Ditto with Gauron, only it's Sousuke + Kaname = One very pissed off Gauron. It doesn't even have to be with Kaname. Sousuke + anyone else (including True Companions / father figure) = very pissed off Gauron. As far as Gauron is concerned, Kashim should not be with anyone else.
Yui in Fushigi Yuugi is jealous of both Tamahome and Miaka, constantly trying to come between them.
Takuma Fudou from Get Backers is shown to be this... and not towards Ban, but towards Ginji. To elaborate, he's jealous of the attention that Ginji gets from Ban, and he actually tells Ginji that he dislikes him because Ban doesn't even notice him when Ginji is around. He then proceeds to try to Murder the Hypotenuse while telling Ginji that Ban's eyes aren't on him because Ginji is in the way.
In Goblin Slayer, when we get a chance to see the perspective of the goblins, it's revealed that the goblin psyche is one part a total Lack of Empathy to one part an insatiable envy, and a resentment of all things better than theirs, mixed with a complete refusal to actively try to help themselves get better. They steal whatever they can, let it get destroyed from lack of maintenance, and do nothing but curse others for having nicer things. A good illustration of this comes the Goblin viewpoint chapter in Volume 4, where a goblin who took a spear from a captured adventurer decides he wants the belt his brother took instead, only to become outraged and possessive when he realizes his brother wants the spear as well.
Wendy Garret of GUN×SWORD displays jealousy whenever other women show too much interest in Van. (She's also green-eyed, but that's probably a coincidence!) It is just possible that some of Van's dislike of Joshua also falls into this trope, but that may be a stretch.
This is why Natsume from Hidamari Sketch is often such a jerk to Sae: on the day on the entrance ceremony, she found herself having to go alone, the train (which normally takes 42 minutes on top of the 10 minutes by bicycle) had to make an emergency stop, she took the wrong street, and finally, she found the shoe locker she thought was hers to be full. Sae directed her to the next set of lockers, and they talked as they hurried. Now, Natsume latched on to this, thinking that they might become best friends. She was unable to meet up with Sae, and didn't see her until ten days later, and upon greeting her, found her with Hiro, who was in the same class and apartment. This triggered something inside her, and, well... she realized as she sulked after her initial outburst that Sae didn't do anything wrong, but that didn't prompt her to change. (As a side note, Natsume does have green eyes.)
Is the Order a Rabbit?: Just a very subtle one, but in episode 6, Chino feels left out when her two school friends, Megu and Maya, spend a lot of time with Cocoa and Rize at the Rabbit House. When she tells Chiya about it, the latter notices the former is unaware of the feeling of loneliness when she saw all of them like that.
In Love Roma Hoshino has been jealous of Negishi's old classmate.
In Lovely Complex Otani was jealous when Risa had a crush on Maity sensei, leading him to realize/confess his feelings. Later, he is also jealous and possessive towards Risa on several other occasions. To say nothing of Risa, to a lesser extent, over Otani as well. Then there's Mimi who is a Yandere over Otani. She gets better, though.
In Magic Kaito Kaito was jealous that Aoko felt safe with the teacher while they were exploring the school after dark and that she didn't partner with him and that she didn't seem bothered by Hakuba asking her out.
First off, we have Yamano Taishou who is a strange case. At first Taishou is jealous of Buchi because Buchi was getting so much praise in school. Then he gets jealous of him when he learns that his foreskin has pulled back, while his own foreskin hasn't pulled back because he has phimosis. He was going to embarrass Buchi by taking nude pictures of him and releasing them at the school, but when he sees an old picture from when he first met Buchi, he decides to not release them.
Then in the second volume, Taishou grew jealous of Buchi because he was working on a school project with Fukami, even though he really wanted to work with Buchi. It doesn't help that Taishou and Fukami never had much of a strong friendship so Taishou didn't like Fukami much. When Buchi tells Taishou that he is his friend just like Fukami, Taishou felt that Buchi was comparing him to Fukami which got Taishou really upset. It results in Taishou raping Buchi due to Taishou taking out his envy of Fukami on Buchi. Fukami discovers what happened and he punches Taishou to get him to stop. When Taishou finally realizes that he raped Buchi, he immediately regrets it and breaks down crying.
Then we have Amanuma Shinichi who is quite an extreme example.
First he was jealous at the fact that when he got into a top middle school, that he wasn't a top student like he was in elementary school which led to him dropping out of that school and temporarily becoming a Hikikomori.
When he became a Hikikomori, he pretty much became jealous of everyone because so many people thought that he would be a top student in a top middle school, but instead he ended up dropping out of middle school and he felt that everyone around him saw him as a failure. He even felt that his own parents saw him as a failure.
When he transferred to Buchi's and Taishou's middle school, he became jealous of Taishou because back in first grade, he bullied him a lot and he thought that it would have affected him a lot in middle school. But he was surprised to see that Taishou was just about an average middle school student, while he had everything that happened to him.
Captain Brian, Lostman's superior in the Navy in Moonlight Mile. Annoyed at being repeatedly shown up by Lostman, he intercepts the orders for him to be transferred to NASA, refusing to release him from his command without flying one last mission for him, stating that while flying the Shuttle is more honorable than flying fighter jets, until the orders go through, Lostman is still a soldier, and a soldier's highest duty is to risk his life for his country. Then he lets Lostman get shot down. Lostman's lost behind enemy lines for over a year before he comes back, by which time he's joined NASA... and Lostman ends up his SUPERIOR.
Katarina was supposed to be super envious of Maria for her talent and winning Gerald's love, but now that she's suddenly nice and doesn't like Gerald much she has no jealousy at all, making her immune to some forms of dark magic.
Katarina herself is the target of jealousy for people who envy her position, large number of importance friends and that she's engaged to royalty, but these very traits make it basically impossible to bully, harass or target her. They don't even bother trying without being manipulated by magic.
Nadia: The Secret of Blue Water: During the Nautilus episodes, a triangle of jealousy emerges between Grandis, Electra, and Nadia... for different reasons. Grandis is jealous of Electra's love for Nemo. Electra is jealous of both Grandis's attraction to Nemo and Nadia out of her own fear of losing Nemo (she tries to suppress it, though). Nadia, meanwhile, becomes jealous of Jean's friendship with Electra, to the point where she fears she may lose him to the latter (when in fact, nothing romantic is happening between either). Even Sanson is somewhat implied to be jealous of Captain Nemo at one point... although partially out of fear for Grandis' usual amorous fickleness and failed love affairs.
Sasuke grows jealous when he discovers that Naruto is advancing faster than he is, eventually completely annihilating his better judgment and going off to join Orochimaru. It just goes downhill from there.
This jealousy was spurred on by another bout of jealousy. Sasuke was jealous that Itachi had focused his attention on Naruto rather than him, even if that attention was entirely negative. This spurred him into fighting Naruto, which revealed the difference in their strength.
In turn, Naruto was this towards Sasuke, but only in Part I. He was jealous of Sasuke's skills and reputation, and he was jealous that Sasuke was the one Sakura had a crush on. However, his jealousy towards Sasuke ended in the middle of Part II, after he finally achieved his lifelong dream of being acknowledged by all of Konoha upon him defeating Pain, after his "feelings" for Sakura finally came to an end when she gave him her fake love confession and he rejected her outright in Chapter 469, and after he finally admitted to Sai and to himself that he always knew Sakura only ever loved Sasuke and would never love him romantically in Chapter 474. Sakura calls him out on this in the canon movie The Last: Naruto the Movie, stating that his jealousy towards Sasuke, his desire to beat out Sasuke at something for once, was the only reason why he had a crush on her—which was implied in Chapter 3.
Lee gets jealous of Naruto and Sasuke despite having curbstomped both of them; the former for defeating his rival Neji, and the latter for getting to fight Gaara in the finals and having the Sharingan.
Asuka becomes jealous of Shinji for his apparent skills at piloting, and of Rei for believing Shinji feels closer to her. Misato gets very jealous whenever Kaji sneaks off to flirt with other women.
In the manga, Kaworu is jealous toward Rei, as she and Shinji are very close in this continuity while he harbors feelings for him and Shinji himself refuses to admit that he does like him. Kaworu has a sarcastic attitude toward her and doesn't feel anything for her death, although it's partly because he operates entirely on Angel's logic and the fact that her main motivation is saving Shinji and not him.
In Nijigahara Holograph, Maki admits to her boss her reason for going along with the plan to drop Arié down the well into the Nijigahara channel was that she liked Kohta but Arié was drawing his attention away.
Interestingly Usopp could be low-key jealous of the Monster Trio at times, at one point he gets childishly annoyed at Zoro for making him look like pathetic on Drum Island. This becomes story relevant around Water 7 as Usopp feelings of inadequacy and uselessness compared to Luffy, Zoro and Sanji culminate in him fighting Luffy and leaving the crew and only returning once he's seen the value inside himself and apologized.
Tashigi has bitter feelings towards Zoro whom she considers a rival over the fact he doesn't fight her seriously and how much stronger he is than her as well as possessing a Legendary sword that she wants. There's also suggested other feelings she doesn't admit.
Sanji is a more straightforward example as witnessing any male having better luck with women than himself instantly causes this reaction to point of him being a Crazy Jealous Guy. Seriously at one point in the anime Sanji gave a downright scary Death Glare towards the eight year old Momonosuke while he was chatting innocently with Nami◊... though to be fair Momonosuk is a Dirty Kid, something Nami is mostly oblivious of.
The Bear King the Big Bad of Movie 2 gave Sanji this look, when he learned Nami (whom he wanted to marry) let Sanji rub suntan lotion on her naked back causing Bear King to beat him around and then have Sanji publicly crucified out of sheer jealously.
Luffy a true Manchild was a Green Eyed Monster of Nami's Waver skills in Skypeia especially as he nearly drowned when trying to ride it, while everyone was praising Nami's joy ride Luffy stuck his tongue out and hoped she'd sink.
Zoro of all people had a small moment of this in Alabasta when Sanji had a Big Damn Heroes moment rescuing the crew in Rain Dinners, while Luffy, Usopp and Nami were joyous Zoro literally gnashed his teeth and told Sanji to stop screwing around and get them out of the Sea Stone cage already.
Blackbeard invoked this when Thatch found Yami Yami no Mi Devil Fruit, he even killed Thatch just get the Fruit since he desired it so much.
The Fighting Narcissist Cavendish was a Green Eyed Monster to the whole Worst Generation aka 12 Supernovas for being more popular than him, he attacked Luffy multiple times and even after his HeelFace Turn he was still jealous of Trafalgar Law.
Franky became violently jealous of Usopp when he got a higher bounty than him, it must be pretty frustrating given Franky is a badass Cyborg while Usopp is a cowardly almost Non-Action Guy.
During the escape at the Tea Party on Whole Cake Island Charlotte Pudding gives a questionable look◊ when Sanji holds Nami in his arms. True she could be just shocked at their escape but considering her burgeoning feelings for Sanji, it's probably something else.
Peach Girl revolves around this Trope. Let's see...
Sae is jealous of Momo to the point of hating her, but she possibly admires her as well, otherwise she wouldn't fuck with Momo's life so much, and try to steal Toji away from her. Toji and Kairi are also jealous of each other because they both are competing for Momo's attention.
Pokémon: The instincts of wild Pokemon drive them to fight over food sources, territory, mates, etc. But wild Pokemon often attack domesticated Pokemon out of nothing more than jealousy. Given that the latter get 24-hour healing, food and protection for doing nothing other than what all Pokemon do naturally- fight- it's not hard to see why.
Misty often invoked this when another girl was interested in Ash.
So as Serena.
In The Prince of Tennis, Tomoka's jealousy of almost any girl who talks to Ryoma (aside of Sakuno), Kamio's jealousy of any males who get too close to his crush An, and Yuuji's possessiveness of his partner Koharu are quite played for laughs. In the manga, Sakuno also has a brief moment of jealousy when Kotoha from Tsubakikawa appears and claims to be in love with Ryoma, but unlike the others she manages to set it aside.
Yuuta Fuji's jealousy of his older brother Shuusuke and Kurumi Iijyuin's jealousy of her older twin sister Narumi make both of them rebel against their more succesful siblings. A big part of Shuusuke's earlier Character Development is tied to him first hiding his own pain and later managing to resolve the issue with Yuuta; later, he uses his experience to help Kurumi reconcile with Narumi.
In Revolutionary Girl Utena:, the very green-haired Kyouichi Saionji is the personification of envy. He's envious of his best friend and classmate Touga because he seems to be better than him on every field, he's envious of the chairman Akio because, well, because he's the fat cat, and he's envious of Utena because hey, she defeated him, she got Anthy as her "bride" and she's now the "official" Prince... on second thought, poor guy. Okay, maybe his eyes aren't green, but he has a "green" theme going on (hair, pants, duelist rose).
This is also Shiori's motivation. She felt inferior compared to Juri, so she began hanging out with her to manipulate her feelings, culminating in stealing a boy who wanted to ask Juri out. The real tragedy is that this worked and turned Juri into a Broken Bird... because she was in love withShiori from the start.
Sailor Moon: Usagi towards any girl who expresses interest in Mamoru. Queen Beryl, Galaxia, the anime's Ann, and Nehellenia are jealous of Usagi because of her romantic involvement with Mamoru. Then there's the anime's Ali and Prince Diamond, who are both jealous, to a T, of Mamoru. Finally, Zoisite is quite a literal example where Kunzite's concerned, getting offended anytime Kunzite shows affection or attraction to anyone who isn't him.
Emerald/Esmeraude actually takes this trope further in the original anime when her jealousy (primarily directed at Sailor Moon over Diamond/Demande's affection) is exploited by Wiseman to turn her into a dragon.
In Skip Beat!, this is explicitly shown as the reason Kyouko didn't have any female friends back in elementary or junior high school: since she was too close to School Idol Shou, the other girls outcasted her. Several other characters in the series have this as part of their personalities: Shou towards Ren, that Rich Bitch against Kanae, a certain band leader toward Shou...
In So I'm a Spider, So What? Sophia was envious of Wakaba Hiiro in her first life for being beautiful and stand-offish without being ostracized like her. In her second life she becomes envious of Shiraori for her strength, which extends to anyone stronger than her and eventually results in her developing the EnvyRuler skill.
Soul Eater has the Envy chapter of the Book of Eibon, although we only see what Soul and Maka have envy for; Maka is jealous of Liz and of music itself, since Soul loves it so much while she can't even understand it, despite studying it ad nauseum. She's also jealous of/worried about other meisters who claim to fit Soul better - especially girls. Soul is jealous of his older brother, Wes, for his superior musical talent. It is also implied that he chose to be Maka's partner because she didn't understand music, and he feels guilty for that. What makes this even better is that Maka actually has green eyes.
In Strawberry Marshmallow, Miu often feels jealousy over Nobue's preferential treatment of Ana and Matsuri, and sometimes competes for her attention even when she's trying to take care of her sister when she has a cold.
Tekkaman Blade: Tekkaman Evil/Shinya is loved by his family, but feels like he's being considered the weak one as the 'good' treatments was given to Blade/Takaya, for instance, when they both were nearly drowning, Shinya was saved instantly, but Takaya was told to just save himself... yet Shinya was JEALOUS because the family trusted Takaya's strength over his own strength. Kind of complicated, yes.
In Tokyo Crazy Paradise both Ryuji and (eventually) Tsukasa have been jealous when the other showed any interest in anyone but them.
Tokyo Ghoul: Kanae seems to harbor an intense jealousy towards Chie and Sasaki, simply for having Tsukiyama's interest.
Uchi no Musume ni Te o Dasu na! provides an incestuous example. In the "Amazing Eighth Wonder Vol.1", Hanna tells Athena why her daughter, Clara, is upset with her. Ever since Athena's reunited with her husband, they've been making up for lost time every night, and Clara can hear them; leaving her feeling jilted, because she has the hots for her own mother.
In UFO Baby Miyu has been jealous of Kanata's old childhood friend, and Kanata jealous of that older guy Miyu had a crush on.
In the live-action adaptation of Uzumaki, it's Mitsuru, one of Kirie's schoolmates, who becomes this. He practically makes deep gouges on the tree he's hiding behind while watching Kirie and Shuichi, and the look on his face is that of sheer jealousy and hatred towards Shuichi.
Yu-Gi-Oh! GX: This is the entire premise of Season 3 in a nutshell. Yubel, once Judai's best friend and protector in a past life, has been corrupted by the Light of Destruction (ironically because he sent them there in hope that it would make them better) and now they come back as an insane, crazy-in-love Self-Proclaimed Love Interest who hurt Judai thinking that it's how they should "love" him, and show huge amount of jealousy over his closeness with Johan. Thankfully, they get better after he remembers their past and promises to love them once again.
Yuru-Yuri: Sakurako becomes the very definition of this when Himawari spends time after school teaching Chinatsu to knit a scarf for Valentine's day instead of tutoring Sakurako. If this weren't a typical comedy anime, the episode probably would have ended with them becoming an Official Couple.