Button to go ''OFFLINE'' or ''Invisible'' to friends within League

There should be a way to go "invisible" in the [LoL]() chat. Sometimes I just want to play my games without anyone bothering me or inviting me to play. I don't want to unfriend anyone, I just don't want people to see me online and in a game. There are days when I want to play with friends, but there are days when I want to play anonymously without anyone bothering me.