The root of toxicity
I think I've figured it out, boardfolks. Trash talk and taunting and bad attitudes are all just the faces of toxicity in League. Figureheads, if you will. Through my own independent research combined with the efforts of a joint research study conducted by NASA and CDC, the underlying cause became abundantly clear: "ggwp" and its more well-known identity of simply "gg".
False sincerity in video games has reached a record high in recent years due to this phrase alone. There are so few instances of a so-called "good game" that to apply it to the average League game (a completely one-sided match) is not only wrong, but an insult to the losing team! It is one thing to call them out directly about how they fucked up. Maybe they chose the wrong Champions, or perhaps they made poor decisions in the game. In rare occurrences, Junglers will forget to take Smite. Yet to insincerely tell them they did a good job adds insult to injury and then rubs salt-covered barbed wire into the wounds so that you can walk away feeling like a good person. Statistics have proven that players who receive "ggwp" from their opponents after a game tilt 73% more than players who win. GG leads to tilting which leads to a new, stronger salt, which in turn breeds toxicity.
I think the truly sportsmanlike solution for this is to not lie to your opponents. It's to tell them the truth, such as- "Nice try, but you've got to actually be good at the game to beat us!" Maybe even personalize it against your laner, just as long as you remind them that they lost, without trying to make them feel better about it. Will this solution solve these problems immediately? No, but the only other option would be to remove Yasuo or Lee Sin or Vayne or Caitlyn, and we need them! If they're gone, Riot might buff someone like Aatrox or Karthus.
Sources:
When to stop maining Fizz, by Dr. Jonathan Quentin Arbuckle Has being nice gone too far?, by Dr. Ted Turner, Environmentalist Guy Fieri deems salt 'Too salty', by Dr. Phil McGraw