Some ideas to help with player behaviour issues and avoid tilt
With the season 6 changes to champion select coming up, it's great to see that Riot is implementing measures to eliminate factors that can contribute to hostilities between teammates going into games. You no longer have to be worried about not getting a position you don't want to play. Players don't have to worry about auto-lockers between 2 people picking on the same turn. Players will not feel the need to bash someone about how much better the team would be doing if they let them have that position. This is all a great start to addressing poor player behaviour before it manifests.
To further these goals, I feel that measures can also be taken in-game and after games to improve player experiences.
Remove Post-Game Lobby Chat
If you like what someone did, you can honour them. If you think someone behaved poorly, you can report them. If you really feel the need to tell someone how great they were, you can send them a friend request. While many of us will move onto the next game. There are some that don't. Some players will sit and flame whoever they think didn't perform to their standards, while PC Principals incarnate will complain about how abusive someone was in-game or argue with the instigator. We should just remove this feature as you're essentially done dealing with your teammates when the victory/defeat screen comes up. Why is this such a big deal? Because the players that flame/respond to the flamer get worked up, then queue up for another game. Removal of the chat after the game would stop whatever went on in-game from escalating and potentially affecting the subsequent game.
Promote The Mute Button
If someone is being verbally abusive in-game, you don't have to sit and read it. Mute them. Even if it's directed at a teammate. Mute them. If you think it warrants a report then report them after the game. If the evidence is there after enough reports they will be dealt with, you don't have to sit and personally record everything they've said. Better yet, stats on how often players are muted in-game could contribute to the process of flagging accounts for review. Why should we be promoting this feature that's been in the game since it's conception? Because we should be focusing on playing the actual game instead of feeling the need to witness an episode of Days of Our League between players in chat, Both the actions of our classic toxic players and those of the PC Principals change the match from a game of league of legends to babysitter simulator 2017. People have to tell teammates to just play the game and now are focused on the hostility between the two players instead of the game. So now you have a team of unfocused people. Maybe provide action that people can take in-game. When you mute someone, a message could appear to everyone except the person muted. "A player has muted <insert champion here>. Disruptive players detract focus away from the game at hand." This in itself promotes the use of the mute button in-game without having to type anything and potentially escalate the situation more by telling someone to mute them. During the game is not the time to try and work through issues and attitude problems. There is no reason for players that are muted to know they are muted either as it would just aggravate them more in-game. If the whole team mutes them, then now you have up to 4 people that can get back to focusing on the game instead of focusing on what that one player has to say. And if everyone starts muting a champ, others will follow so situations diffuse instead of continuing to escalate.
Remove Mastery Badges From Ranked Loading Screens
Nothing says tilt more than seeing someone is playing Vayne for the first time in Ranked. Have it displayed in the post-game screen. Again this is removing factors that can lead to hostility between teammates. If a teammate is a first time Vayne and goes 21/0/15, no issues. If they go 1/21/5, not only may people be annoyed that you're feeding, but they haven't even played sufficient games on that champion and they're picking them in ranked! Seeing a low tier icon in the loading screen just gives them something else to flame about.
Team Milestone Announcements
League of Legends has been moving towards being more team-focused rather than having one player consistently carry the whole team. Announcements do not reflect this. It's great to have kill streaks announced and acknowledge individual accomplishments, but team accomplishments could be used to inspire players on their respective teams. Blue team does a big play and gets a lot of gold, but was behind? Then blue team could hear "Blue team is closing in". If Red Team is ahead then Red Team could hear "Red team widens the gap" after a big play. Something like this could be used to motivate players, make them feel a little better and maybe make a few people less likely to flame their team. Just some positive feedback for the players to help relieve tension. You only see your team's accomplishments. Some game stats could also play a role. Every X number of enemy wards destroyed could have something come up. When teams reach the cap of number of pink wards on the map. Other than providing a positive atmosphere, even if you're behind in gold, these team milestones would also help players develop better habits.