Subverted by Ginger from Collar 6, who sports 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, the settle for a happy, trouble-free OT 3.
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.
Pibgorn Dru's fatal flaw — alas, usually someone else is the fatality.
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.