Report system
As we came to some sort of understaning in this post, and while I agree that this exact problem is not a major one and the system is never perfect, we can partially solve it and many related ones by motivating people to report responsibly - not "every time somebody makes you uncomfortable" and educate the community in the process.
Nowadays the report system begs to be abused. It's evident from the fact that "report" is one of the most(if not the most) typed words in league, despite the fact that Riot Games clearly expressed that they don't want people to ask for reports, which might be the most specific rule they ever had.
You can report anyone for anything without second thought and the system will try to find a reason, its own one. It's one click away. Some premades do that to each other as a joke without even knowing how it functions, leading to posts about getting punished for intentionally feeding or "zero tolerance" stuff when it wasn't meant to be punished. Hell, you can even report the wrong person by accident.
I think it should be made a simple, but much more thoughtful process, make people actually file the report - not just faceroll through endgame screen. Here is what I propose.
For chat-related offences present people with the full chatlog of the person to be reported. Each message can be flagged to be reviewed for offensive or negative speech.
For gameplay-related offences make people go through the replay and choose time intervals with violations.
People abusing by repeatedly marking the whole game or entire chatlogs should receive a friendly reminder that their reports can't be accepted that way.
People repeatedly flagging innocents should receive an automatic tip that the behaviour they mark is acceptable and/or can't be determined to be punishable with enough certainty.
When IFS learns enough, Riot can start sending the examples of such reports back to the player so he can see what he is doing wrong. There is no need to punish players for that.
I think this would educate people on what is right and what is wrong. Within such moderately time-consuming system we can display tips about everything related to the punishment system, like what is punishable or the fact that you shouldn't ask for reports. I also like the fact that this system's design guarantees that the enemy team can't report someone for the chat they don't see, directly affecting incentive to call for reports.
Just as always, you are welcome to point out what am I missing.