Sakura herself has been bashed by a few fans for picking Syaoran instead of Tomoyo and for being oblivious to the latter's more-than-friendly affections.
Kaho Mizuki, Eriol's canon love interest, is hated by two groups of shippers: Eriol/Tomoyo fans, and a smaller group of Touya/Yukito fans. Mizuki's romantic history with Touya occurs well before the story; in the story, Kaho is very supportiveof Touya's new relationship. There's also a Hot for Student aspect to her relationship with Eriol that squicks people who forget or deliberately ignore both Eriol's true age and that she never was his teacher. In Eriol/Tomoyo fic, her only role is usually to leave Eriol without warning and never return, based on how her relationship with Touya ended, even though in canon she did reunite with Touya and become friends as she said she would when she first left.
It reaches downright disturbing degrees when the Nakuru haters start remarking on Nakuru being actually a genderless magical being who chooses to identify as female due to liking girlish things/outfits/etc. better to make her less "worthy" of Touya's affections. It's creepy because it's easy to see that this is bcause they hate her so much that want to make her look less like an at least seemingly-human person with her own will/thoughts/etc. ... and more like a "thing" without any personality or will just to favor Touya/Yukito! "Un-personing" someone like that for no reason other than DFOS is horrible.
Yukito sometimes gets bashed by Touya het-shippers. They call him a boring, shallow, too-perfect Mary Sue who is completely superfluous to the plot and say he could have been killed off or merged with Yue after the first arc with no complications.
While Sonomi does canonically resent Fujitaka's marrying her beloved cousin Nadeshiko, the man's been called an "evil bastard" for "ruining Sonomi's life" even though he's canonically portrayed as a good man and a wonderful father who loved his wife and loves his kids very much. (Or how Nadeshiko didn't owe Sonomi any romantic affection and willingly chose Fujitaka, even facing disownment from her family.)
Be careful mentioning Yuuko Ichihara around Clow/Yue shippers. Really careful. In fact, it might be best to avoid all mentions os Tsubasa and Holic at all. Or Mokona's.