My Thoughts on Reformation
(Foreword: This isn't about the still-vague system Riot uses to determine eligibility for Hextech Crafting, but it could prove useful to people looking to get back into that game. This is about general reform, and improvement not just of individual players, but of the players they meet as well.)
When someone thinks of reforming, they might think of putting on a happy face and just taking whatever other people say. That's only partially right. Reformation is about looking at what bothers you, and coming to terms with how to remedy or avoid it in a productive manner. Show that you've learned not merely how to ignore the problem, but also how to chip away at it elsewhere.
If teammates are arguing over something or other, let them know that they're only hurting their own chance to win the game by doing so. If this doesn't convince them, don't press the issue any further or you'll just be falling into the trap. If you happen to lose the game in question, rather than let it get to you, take pride in the fact that you did what you could and that those players lost to both the enemy team AND themselves. If you win, be sure to let them know that future wins would come easier without pointless arguing.
If you don't say anything factually demeaning or personally offensive, you don't need to worry about reports. Being reported for "constructive criticism" will hold little weight, and if you somehow DID get into trouble, that's what chat logs are for. In that sense, the report system is like a sharp object. It does useful things when used properly, but you won't get much use out of it if you're too paranoid about it cutting you.
If you find yourself with a ban, use that time to think of productive and unobtrusive ways to combat the problem rather than spending days/weeks griping about "that player" or "that team". You're not doing yourself any favors and defeating the entire purpose of the ban if you dwell on the negative.
Obviously, just one person doing this doesn't make much of a difference. However, one bolt doesn't make a working machine either. The more people that get in on it, the more bolts you have towards that working machine. It's a slow process, and you don't know for sure if it'll work out in the end, but it's better to move forward than to go nowhere or even backward.
Humans are a social species that thrives on interaction and building off of one another. Don't let this game take that away.