Harry Potter. People often talk about a "golden age" of JK Rowling, and I think to myself, what golden age? Harry Potter, both the character and the books, are written like a hyperinflated Cinderella, complete with an attempt at discriminatory apologetics that would make CS Lewis say "you okay bro?"
Also, Luke Skywalker. People hate Anakin for being whiny and weak and Rey for being a Mary Sue, but Luke is both and nobody complains.
Astarion from BG3. I can understand why people like him. I personally do not and generally never used him in the party because I didn't want to hear him be annoyed yet again I was helping people.
Sephiroth. His look is basically the most generic bishy anime character you can make, his entire backstory can be boiled down to "mommy issues" and his motivations are the standard villain "destroy world/become god". He's just so bland.
We get it. You wish a dashing eccentric gentleman with an English accent will appear out of the blue and whisk you away from your situation to a life of adventure. But it's not going to happen, sweetheart.
It doesn't help that Doctor Who has always been crap sci-fi, but gets a free ride due to having such a long history stretching back to before anyone knew any better. The series as a whole is one of those I find also dragged down by a subsection of rabid insufferable fans, at least the modern incarnations, right up there with Rick and Morty and Supernatural. (I see I already kicked the beehive.)
I really don't get the obsession with overusing the Joker when most of Barman's other rogue gallery members are much more interesting. The worst of it is during "The Batman Who Laughs", because now you have both the regular Joker and "what if Batman became Joker" running around. And then, as if it couldn't get any more ridiculous,
spoiler
The Batman who Laughs gets Dr. Manhattan's powers in a groan-worthy way which is like, not how Dr. Manhattan works at all just so they can fit more Joker into the story.
And I think most people will agree by now that Harley Quinn is a lot better of a character after she's done being Joker's sidekick.
There are a few companions in Mass Effect that seem to inspire a way stronger reaction from other fans and I don't totally get it. Like, I like Thane, and I'm sad about what happens to him, but some people are SO into him and I don't get it. I also love Tali and restarted my first nearly complete playthrough when I realized I couldn't save her and Legion, but there are fans who are full on obsessed. Then again, my love for Garrus can't be contained, so I'm sure some people don't get that.
At least we can all agree that Ashley and Kaiden are the worst, right?
Edward Kenway from Assassin's Creed 4. The whole game actually is extremely overrated. I had a hard time finishing that game. I rather play 3 or even Unity.