The word has lost almost all meaning in this day of society.

When this is reported. I believe that the way its used, should effect the reasoning for if it should be worth infraction/ban

If they go out of their way and call you or say "Sup Nigga" or "You stupid nigga/nigger". That is indeed, infraction/ban worthy.

If they just say "My Nigga" or "Nigga, we blah blah blah". That seems okay.

If you can tell its indeed an insult nontheless, and not just friendly conversation. Then take action.