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I'll get straight to the point.
You agreed to the Summoner's Code, if you haven't, you should because if you act a fool more than likely you will get banned easier. The code is a chance for everyone that has a few bad games to not get punished. Abide by it.
The Summoner's Code also mentions these topics for those who haven't read into it much:
Support your Team
Drive Constructive Feedback
Facilitate Civil Discussion
Enjoy Yourself, but not at Anyone Else’s Expense
Show Humility in Victory, and Grace in Defeat
Be Resolute, not Indignant
Leave No Newbie Behind!
Lead by Example
Personally, I am trying to abide by all these points to build better character for myself and not ruin someone's mood in the game. It is easy to be a jerk, but hard to be nice. So, I just try to have patience and work with everyone on my team, whether we win or lose.
The two most important points I believe, are the last two. We as a community, need to lead by example and help any new players without being rude or acting like we are the best players in the world, like most players do in this game. Wake up call: You're not. Even if you are a high ELO like 2400, if you're not competing in major tournaments or events, you're NOT one of the best players in the world, sorry. Regardless, even if you're really good you shouldn't act like a jerk.
So what is my point here? It is up to us to lead by example, stop talking trash, and work with others even if they are new. How do you know people aren't on new accounts and not smurf accounts? You don't know unless you know the person beforehand, which is hard to tell most of the time. So treat every "smurf" as if they were a new account.
I have been doing really well of not talking trash to my teammates or the enemy and reporting people who need to be reported. That should be it. The rest that everyone is adding into the chat or game, is not needed. Don't act like you're the #1 because unless you're a tournament pro, you're not. Even then, you should abide by the code.
tl;dr abide by the summoner's code, help out new players even if you lose the match, don't talk trash, say gg without the "noobs" at the end, and report players if need be.
It is time the few who want to do the right thing let the others know that you're not alone.