Here's the thing though: You and your brother are not the only players in the game, as depending on the mode you have 1-4 additional teammates as well. Besides, racial slurs are something that are never allowed period, and you being reported and banned for it doesn't mean that Riot is going down hill (they're not), but that the other players didn't appreciate you using a racial slur, and since you violated the zero-tolerance policy (and possibly have other recent infractions as well) you received a 14-day ban. In the future if you want to joke around then refrain from using that sort of language and behavior, or at the very least stick to private chat or a full pre-made where you know you won't get reported for using slurs. The punishment won't be overturned.