Ridiculous and weird body or face proportions, when the MC is an asshole or violent towards LIs and terrible writing or too many spelling and grammar mistakes. Might be some more things as well, but if I see any of that I'm out.
I'm way too socially reserved and have too much trust issues to share with friends, but with SO I can share small things by fishing for what they like first. I don't think I'll ever share everything with someone unless an SO tells me they like similar things to me first 😅