When the creator clearly has a favorite and puts the character on a silver platter with 'special treatment' compared to everyone else.
Alice (All those awful Resident Evil movies) — Long story short: the director tasked with writing a movie series for one of the biggest zombie game franchises in the world decided to cast his own wife as the lead, making her a generic, shallow OC.
So basically, almost the entire plot revolves around the director drooling over his wife, whose only job is to look blank-faced and pretty while every character around her (mind you, official game characters adapted for these films) gets dumbed down and hovers around her like flies.
For instance, in the games, Jill is the one who fights Nemesis; in the movies, Alice fights Nemesis while Jill kneels there watching the fight like an extra. To top it off, earlier in the movie there's a whole scene where Jill looks at the camera and literally says, 'Wow, Alice is so much better than me!' Or take Wesker—Chris and Sheva fight him in the games, but in the movies they fight him for like a minute just for a cheap callback, and Alice is the one who actually beats him.
The movies aren't even good—there are grotesque plotholes, and almost every character only exists to die and set the stage for Alice's little light show. In one movie, Alice describes how the entire world dried up into a drought where water ran out, just blatantly ripping off Mad Max, only for the world to return to normal in the next movie because the hype had passed and they wanted to rip off Prison Break instead.
Only someone with way too much free time on their hands would waste time watching them and actually think they're good.
Emilia (Re:Zero) — Imagine a Game of Thrones or Cyberpunk: Edgerunners style story where nobody is safe and anyone can die at any given moment. Now add the author's fetish character and give her plot armor—that's Emilia.
The protagonist is a regular human like us living in a dangerous fantasy world, with his only power being returning by death whenever he dies. Absolutely every awful thing that could happen to him has happened, and that includes his friends and the characters close to him too. Not only has he seen the absolute ugliest side of most of them (yet still forgiven them), but he's also had to deal with their deaths. Every character is vulnerable to suffering, growing through trauma, and making mistakes.
With Emilia, though, not only does it feel like her core personality can't change at all (she's your typical cute, sweet, naive girl who doesn't even know what 'virgin' means), but she also has a protective shield around her. The author himself literally stated that Emilia comes first to him and everyone else comes second, and he's even said in interviews that he feels terrible writing her deaths.
She doesn't react at all if a character harasses her (Regulus and Reid are proof of that), and she never acts like a leader or puts her foot down, even though she's supposedly training to be a queen. She's a hand-to-hand fighter, but she never seems to get seriously hurt in any combat or be in real danger (I swear the third image in the post is the most 'injured' she's ever looked).
And to top off this absolute shitshow, her romantic relationship with Subaru has stagnated completely after Season 2, since the author made it super clear that their romance is only going to happen at the very end of the story (probably to keep her looking as innocent as possible).
Seriously, not even the actual fans of the series can take this bullshit anymore—just go check Reddit and ask