Story time.
My friend was a huge pill-popper in high school because his brother was a huge druggie and a terrible influence on him. So he, the younger brother, is rolling on E one night and wants to ride his bike home at midnight -- his house is like... 20km into the country where there are no street lights. And he's high as fuck.
I call the older brother, who's started to go clean. The bigger brother shows up, puts the bike in his trunk, and tells his brother to get in the fucking car so they can go home. My friend refuses over and over and starts yelling. We're all white but he says -- stone-cold, point-blank -- to his brother;
"Andrew, quit being a fucking nigger. I don't even mean anything against black people by saying that. In my opinion, being a nigger means not giving a fuck about anyone but yourself. So cut the shit, stop being a nigger, and get the fuck in the car -- mom's worried sick and this is all my fault."
About the only time I've felt "okay" with it being uttered by a white dude in a negative context. I only feel completely alright with it when it's being used as part of a quote, really.