I really hate when the story's author decides to show up or possess a character so they can tell you what they think or what they believe. I read lately some interactive book and in the middle of the conversation with some character suddenly there is brought up the subject of people writting interactive books. It was mostly cringy, with the whole 'yeah, people that do that sure are amazing! Remember to be always nice towards them..' The whole scene took a couple of paragraphs and just felt kinda cringe.
The other one for me is mostly personal. I hate when there is unique character that know what they want but it is not conforming to the lifescript.txt. Things like being childfree for example. Instead of supporting this character people around just bully them into changing. I love strong female characters that say they don't want children but usually in fiction by the epilogue they already have two, just because they met the Right Man™.
Also! Authors that write their characters to have some unique or slightly niche hobby or job, but they don't understand how it's like to have that certain job/hobby/interest irl. Like, I couldn't finish one book that had its main character as an artist because the author just didn't understand how artists are like. He just made the main heroine extremely pretentious and called it a day. (She wasn't supposed to be read as pretentious and no other character acknowledged this they just thought she was extremely artsy, even her coworkers)