What makes this game change peoples personality?

I know its not a popular topic between lol player. But Im curiouse why player suddenly change their personality after they enter Champselect till they close the client.

And why do people report other player for everything even thoe they did worse:

negative attitude
verbal abuse
Intentional feeding
Always the same report reason. And thats not only one friend that does it.
But at the end of the day i think its League.

What do you guys think about that people change in game.