Telling someone to kill themselves should be an automatic chat-restriction/ban.
I don't struggle with depression or suicidal thoughts. But I know people that have committed suicide and I know people who do suffer with those things. Telling someone to kill themselves is not something that should be taken lightly. After playing poorly all game and being flamed for it from my (presumably duo) top and mid laner I muted them. I played the game out and had no problems, we still lost but that's besides the point. In the post game chat, our mid laner told me to kill myself. I don't take that insult seriously since I don't have thoughts of it but I know that some people out there would and it's completely ridiculous that people can say stuff like that and might not be punished for it.