bigotry against any marginalized group; lgbtphobia, racism, ableism, etc, or support of any conservative/right-wing views or people
sexualizing characters who are minors, or enjoying ships that are pedophilic, incestuous, abusive, or involve real people.
this includes sexual jokes about minors. even if it's 100% ironic and you don't actually sexualize kids, it makes me extremely uncomfortable.
being "neutral" to either of the above points
other
sometimes i block for trivial things like "said smth i didn't like about one of my fav characters" if i feel like it. it's not always over a serious issue.