In No Rest for the Wicked, Beast interprets Perrault's comments about "Beauty" to mean the girl, and that she left him for Perrault. He attacks him in a rage.
In Gunnerkrigg Court, Antimony is jealous of how Kat and Alistair get along. She overcomes it to insist they get a proper farewell — whereupon both she and Kat learn things.
Subverted by Ginger from Collar 6, who sports a green color scheme and is introduced as a possible contender to Laura for Mistress Sixx's affection. However, it is later revealed that while she is, indeed, in love with her "Madame", her feelings towards Laura are less of a jealousy and more of a disgust about her taking Michelle's love (something that Ginger was never able to attain) for granted. Eventually, they settle for a happy, trouble-free OT3.
Wapsi Square: Monica accuses Bud of being envious of Tina. Bud has a bit of a problem with this seeing as she is also a bit envious of Monica and her relationship with Kevin.
In Kevin & Kell, Vin's hatred for Rudy stems from his belief, formed from working as an intern at Herd Thinners, that Rudy has everything he doesn't. He also becomes quite resentful at the end of the Y2k arc when Fenton and Ray reunite with their girlfriends.
Orphaner Dualscar of Homestuck was intensely jealous of Mindfang's romantic liaisons with other trolls - to the point that he murdered her latest conquest The Dolorosa and sold out Mindfang to the Subjugglators, dooming himself in the process.
Bittersweet Candy Bowl has Paulo jealous of his girlfriend's extracurricular activities keeping her away from him, and Daisy jealous of Lucy's success with guys, even though she blows them all off while they all ignore Daisy.
In Urban Underbrush, Clive and Blair's ex-girlfriend foment this at a nightclub. Alas, Clive is actually attracted, tries to kiss her, and gets a brush-off that reveals the truth to Blair.
Part of Ellie's problems with her roommate Quinn in Shotgun Shuffle stem from the fact that Ellie unintentionally stole any chance of popularity from Quinn in the fifth grade, when Ellie came back from the summer with boobs.
In RAIN, Heather's attitude toward her genderfluid sister Kylie is revealed to be this. After a particularly heavy Wham Episode, she reveals that she was born with Complete Androgen Insensitivity Syndrome. Her stepdad once said she was practically a boy, which lead to her resenting Ky for having the femininity she felt like she was denied and that Ky didn't really want herself.
Oglaf has randomly generated page quotes. One is "The god of envy has a better temple than yours."
Bastard!!: While Jin is trying to decide whether to give Kyun up to his dad, he nearly does when he sees her talking to another guy, but decides not to when she smiles and waves at him. However, considering his issues, it may have had more to do with him deciding whether she was worth possibly being killed for than with him being jealous, although he clearly was at least a little bit.
Cursed Princess Club: Aurelia is not fond of how a princess like Gwen, who isn't cursed and has a loving family, is allowed into the club and tries to trick her into doing something that would get her kicked out.
Hooky: Nico's early antagonism towards Dorian was due to jealousy. He saw Dorian as The Ace when it came to magic, while no matter how hard he tried, he couldn't use magic. His current frosty relationship with Mark is due to feeling that Mark has surpassed him.
My Deepest Secret: When Elios sees Emma and Yohan talking, he tries to make her stop talking to him, partially due to jealousy but also because he knows Yohan is on his trail. Later in the series, he begins to try to cause rifts between Emma and her friends.
Sophie is violently jealous of girls with good looks who attract male attention. Emma is one of thesenevermind the fact that much of the attention she gets is unwanted!
A rather literal Green-Eyed Monster appears in Widdershins: in fact, that's the chapter title. Envy is the name of a demonic entity which casually manipulates Dominic Voss, who's desperately envious of Heinrich Wolfe, and, well, everyone else, because they have talents he lacks. With Envy's help, he steals their abilities, becoming The Ace in short order. Thankfully, he does get a crisis of conscience near the chapter's end.
Sleepless Domain: After Cassidy attacks Undine out of suspicion that the latter was responsible for the death of her teammates, she tries to explain her actions as protecting Heartful Punch and the rest of the training club. Bud, however, believes that Cassidy's real problem is that she just couldn't stand Heartful Punch suddenly spending all her time with Undine, and jumped to whatever conclusions would justify acting on her jealousy.