In the case of Dating Sim girls, Tsugumi Obinata from Sanroku no Mystic gets the biggest share of bashing because of her quiet, sweet and shy personality that makes her an Expy of the already maligned Sakuno. The comparisons between her and the more outspoken AyakaTsujimoto from Umibe no Secret always give her the shortest end of the stick, and she's deemed as weaker and stupider... in spite of the fact that she and Ayaka are best friends in-story.
Also, Shizuka Hirose from the Gakuensai no Oujisama game. Completely loathed and accused of being a cockblocking Mary Sue... even when the games are obviously not canon (and neither are Umibe and Sanroku) and you can choose who to pair her with!
Yanagi Renji has been bashed by Inui/Kaidoh fans ever since his and Inui's backstory was brought up, because he used to be Inui's best friend and partner before Inui met Kaidoh and left him without saying anything when his family moved. That's seen as Renji being an horrible and heartless person who hates Inui and wants him to suffer, so his ruthless in-courts behavior (which is a trademark of the Rikkaidai teamas a whole) is "proof" of his cruelty, in spite of it being hinted that he preferred to put a Jerk Ass Facade and remove himself of the picture to not hinder Inui's development as a player.
This happens even when, in the Finals OAV depicting the Rikkai vs Seigaku second matches, Renji goes Kuudere and begs Inui to forfeit the match when he gets injured by Kirihara during their doubles match in the finals, thus proving his bashers wrong. The fact that he's acting emotional in front of Yukimura himself should clue these fans in, but some still insist Renji is faking his concern for Inui.
Inui/Kaidoh fans have also been known to bash Momoshiro, who (it is implied) later became Kaidoh's vice-captain after Inui graduated, by flanderizing his Big EaterandFun Personified character traits to make him an absolute idiot who stuffs his mouth, causes trouble for Kaidoh, and barely does anything else.
We also have the bad treatment Seiichi Yukimura receives from rabid Atobe/Sanada fans due to Sanada's obsessive (and very slashy) devotion to Yukimura, which they see Yukimura being domineering and possessive of Sanada to not give a chance to their ultra-prettified Possession Sue version of Atobe. And some particularly rabid Sanada/Yukimura fans retaliate by bashing Atobe for daring to get in the way of their super-perfect and super-beautiful OTP.
Or the portrayals of Tezuka and Saeki in fics and doujinshii depicting a Tezuka/Fuji/Saeki love triangle, depending on who the fan writer or doujinshi author likes with Fuji the best. Saeki often takes the brunt of it, sadly.
Take this paragraph, replace Saeki with Kawamura, and there you go. Tezuka/Fuji and Taka/Fuji fans were okay at first with each other, but the mutual bashing and specially passive-aggressiveness have escalated with time. And nope, no side is innocent in this: Tezuka/Fuji fans are often rather butthurt for Kawamura's share of Fuji Ship Tease, but the Taka/Fuji fans are prone to be incredibly whiny and victimized at the mere mention of Tezuka and TezuFuji.
An doesn't have it THAT bad, but she still gets pot shots for "stringing Kamio along" and "playing with his feelings" because she's friendly to him but doesn't seem to acknowledge his crush on her. Which brings up rather creepy Unfortunate Implications about how women should "owe" men love because they show open interest on them. (or for that matter, anyone owing anybody else love in such circumstances.)
The hate against almost any female characters in this fandom is (and hopefully, was) so ridiculously strong that even Shioin Higaki from the live-action movie got a share of it. A cute mute girl who replaces Sakuno, plays the flute, is the little sister of Egate Higaki (the guy who replaces Hiyoshi in-story) and forms an Odd Friendship with Ryoma, Shioin immediately got petty "Maaaary Suuuuuue" cat calls from the yaoi-crazy fangirls; it died almost immediately off since this was her only intervention in the POT canon, but it still proves how almost any girl in this fandom will be loathed by the fans.