What ruins stories in my opinion

I just wanted to express my feelings on things that ruin stories.

Harem

Harem makes me feel like the mc is trash.

Making the main character hate everyone because one bad thing happened to them

System

I feel like systems are just convenient plot loopholes to explain powers that the mc gets.

When the people around the mc are annoying. I get having 1 or 2 annoying characters that the mc doesn't like but sometimes it feels a little much.

I don't have any more off the top of my head.