how to report

I have had games where people have been very negative or done things that are dreadful . But when I try to report in the post game lobby, I have no idea which box to check because the actions of the players do not fall into any of the categories, So i end up not reporting because I can't. I could have described the actions perfectly but you need to tick a box to report, It feels weird to me to report someone for the wrong reasons.So I wonder if there is a more broad guide to how to tick the boxes and what goes where would be helpful.