League settings -> In-Game -> Interface -> Turn all chat off (check this) and Turn allied chat off (check this).
Please and thank you.
Chat has never and will never do anything to help you win. Every second spent chatting is a second spent not playing the game and concentrating on what you should be doing, or what you'll do next.
Not once in the history of ever has any league player at any elo read some kind of instructions ("You need to farm better, caitlyn!") and thought to themselves, "Damn... that player is SO right. I'm gonna start farming better right now! I feel so inspired!"
Has never happened. Will never happen.
Instead, they get all defensive and butthurt and personally attacked and start flaming all chat and inting and emoting on the fountain because they're soft, weak, thin skinned, spoiled little babies that didn't get enough ass-beatings growing up like 90% of the league community (and probably 60-70% of the American population)
I turned off chat completely, and went from Silver 3 to Gold 4 in 2 weeks. Instant improvement. Games are less stressful. I enjoy the game more. I don't get angry anymore. I concentrate on my own play, I can think about what I'm doing, I basically treat it like I'm playing with 4 bots on my team -- cuz lets face it, I basically am.
But every so often.... I'll notice my team mates just kinda standing around getting shot by a turret, or getting ganked when they could have EASILY avoided it if they were paying attention. It looks absolutely silly, and for a little while I thought it was connectivity issues or something. Couldn't figure it out.
Then one day it dawned on me....
They're fucking typing. These kids are going full vein-popping rager mode in chat and I can't even see it. Its glorious. I laugh out loud every time, literally. Audibly.
But it sucks to lose a game to some moron who's raging in chat. Sucks to win a game to it too, honestly. Always feels bad to kill someone who's obviously AFK (or in this case, heavily involved with their keyboard)
So just do everyone a solid -- YOURSELF INCLUDED.... and just turn the shit off. Just disable it.
That way YOU don't have to worry about it, and much more importantly -- I don't have to worry about it.