Any kind of animal abuse. I love Celeste Ng but I'm going to skip "Our Missing Hearts" because one of the reviews mentioned an upsetting animal death. I'm sure it's a tiny part of the book but I know it's there and it's completely put me off.

For violence and abuse toward humans, it depends on how it's handled and how graphic it is. There's nothing specific I avoid on principle but I will quit a book if it feels gratuitous. Authors have a right to tell those kinds of stories and I have a right not to engage with the content if it crosses a personal boundary.

I typically don't read horror as a genre (not never, but very very rarely) because if it's too scary I have to sleep with the lights on :)