How to avoid flaming when you're angry
Yup, when you see your midlaner inting you're tempted to write ''report, go AFK, stop trolling kid' and flame. You know why? It's a little psychological trick. Your brain tries to even the situation and release the stress by explicitly showing the annoying factor (the inting person or whatever) that you're being annoyed. We, human beings, tend to verbalize our frustration and find a target to pour our rage onto (this is why sometimes we find ourselves flaming people who aren't even guilty. Your team's doing badly? Well, you'll find yourself flaming the **** outta your jungler because maybe he didn't gank enough). We need a way to express our anger and let others know that we are burning. It's simply how brains work, we can't trick this strategy very often. Indeed, psychologists say it's much better expressing your anger than holding it all in. If you're raging, go punch some pillows and let it all go. However, when we are angry because of a game, the only pillows we can punch are the teammates. Hey, nobody's gonna flame Riot for making Darius too OP, instead we're going to flame our Teemo top getting stomped by a Darius. Our brain is subconsciously convinced that showing the 'guilty guy' that we are upset, the situation is going to change and the guilty guy will suddenly become Faker and carry. But there's hope: we can SHOW our frustration as clear as we want with one simple trick, that won't get us banned (yep, this is what we all care about when we flame, don't we? XD).
Step 1: find a phrase that replaces your typical flame words. Example: instead of 'omg idiot go AFK', choose 'omg A xzu whatever xx'. Something random that's not offensive.
Step 2: OK, you can't simply channel your anger and release it with a non-offensive phrase, cause your brain needs to punch the pillow, not kiss it. So let your teammates know (in a completely FRIENDLY AND FUNNY WAY) that your random phrase is used when you're angry. 'Hey, guys, when I'm tilted I type random numbers in chat, don't mind me'. So now, you teammates will all know that you're angry. Your inting mid will know that, if you're typing those numbers, he's doing something wrong. You let him know this. But it won't be offensive. It'll simply be a confirmation that his plays are... well... not the best.
Step 3: use your phrase. 99% of the cases your team will ignore you, because it's not flame. They won't have the urge to defend themselves and start arguing and go on tilt. They'll just know they're doing something that upsets you and maybe even try to change that. Sometimes they'll start laughing. And trust me, a laughing teammate is much better than a flaming teammate and a permaban.
I started using this strategy, and trust me, it's a very good way to release anger. First, I used 'a'-s in chat, then I switched simply to some SS pings, until I my urge to use the chat and flame was gone. Right now, I am quite tilted again, so I had to develop another emergency phrase. It goes like: 'Hey guys, when I'm angry with you I start typing random chemistry stuff. The longer the words, the angrier I am'. When our Yasuo gives first blood, I type 'carbon dioxide'. When our Yasuo goes full AP and 1/24 and starts running it down mid, I type 'ribulosebisphosphatecarboxylaseoxygenase'.
Hope it helped.