Well I don't find horror disturbing ( I myself am a horror game developer and my horror game does contain a bit voilence ).
The stuff that annoys me most is the shot adult content.
So far I have reported a lot of stuff such as gross visual novel art and disgusting games and assets.
Although it isn't itch's policy to ban this stuff, it is clearly mentioned in the rules that if someone posts adult content without clearly labelling it as adult content, his game will be removed. So a report would work in that case