You may not think someone saying "gg n00bs," "easy game," or whatever is offensive. Regardless, it is against the Summoner's Code, which you all accepted to play the game, and which you're sworn to uphold in the Tribunal. Allow me to demonstrate.
Originally Posted by The Summoner's Code
IV - Enjoy Yourself, But Not At Anyone Else's Expense
Making games is our business, so it should come as no surprise that we want you to have a lot of fun. We want you to get excited, to have tension-filled moments, and to celebrate your success. This doesnt mean that were okay with you ruining anybody elses day.
Remember, taking a jab at your friend in the middle of the game is a lot different than making a glib remark at a complete stranger.
VI - Show Humility in Victory and Grace in Defeat
Having a great game is one of the biggest joys that League of Legends can bring you. But always bear in mind that when youre relishing that landslide victory there is someone on the receiving end that is probably ripping their hair out. While its 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.
Instead, try giving them advice. Example: "Hey, we had wards all over the place and it's obvious you guys weren't buying them. We probably wouldn't be able to gank you so often if you bought a few." Or, failing that, just thank your opponents for the game and move on. Do you really need to make your opponents feel bad for losing? If so, then I don't want you in my games. Neither does the community, and neither does Riot. Whether you feel you're committing an offense or not, you are, and we will be punishing you for it. Best of luck, Summoners! Stay classy.