Show Humility in Victory, and Grace in Defeat
"To be humble to superiors is duty, to equals is courtesy, to inferiors is nobility." -Benjamin Franklin
Having a great game is one of the biggest joys that League of Legends can bring you. But always bear in mind that when you're relishing that landslide victory there is someone on the receiving end that is probably ripping their hair out. While it's alright to celebrate, make sure that you keep any gloating (or any other mode of self-indulgence) out of all chat. Instead, thank your opponents for the game. After all, despite their best efforts, they just made you a very happy person.
This is taken straight from the Summoners code. When you sign up to League, you must accept this