Harassment is against the rules, but it happens to nearly every single player on a daily basis. People who harass other people in game don't even get banned. The only time that anyone gets banned is because of blatant racism and homophobia.
Too often players say literally whatever the hell they want with no repercussions. Just because someone has the ability to mute, it doesn't give the harasser amnesty to the rules of the game. Just because I mute someone, they can't just call me the n-word without punishment.
Riot refuses to do nearly anything about this. Absolutely ridiculous.