[lactau]

>I have a brother. Due to circumstances, I can call him a "stupid idiot" and he will know that I'm not serious and I respect him. However if a stranger calls him the same thing, he will take offense. Is that an unfair double standard?

I wouldn't call my brother 'stupid idiot' in public (neither would I in private by the way). I don't care what you do in private. Though, that's another topic.

When black people call other black people nigga, they don't mean it ironically or as an exaggeration. It is just a word which means black person and which is used only by black people. That's like calling someone 'bro', that's not like calling someone 'stupid idiot'.