2 ideas. the first is that u add "chat" that u send ONLY to the ones that in ur "friend" list. the 2 idea s: BlackList- pepole u hate/dont like. once they are in that list they cant invite you to a battle.
what he wants is an Ignore List(nobody on the list can talk to you, more or less you just cant read what they type), a list of people who are not allowed to challenge you (a No-Challenge list) and a seperate chat method that is private and only to people on a Friend List.
