The philosophy that a single person is granted permission to use casually use a derogatory phrase if one person who is in the group that the phrase is aimed towards does not find offense in it being used. Name is derived from the idea of this concept pertaining to the slur "n*gga," but can also be applicable to many other slurs, such as "f*g" or "tr*nny."
Chris: "Hey, look at that dumb n-gga smoking weed in broad daylight!"
Joe: "You might want to keep it down, dude, that black guy could beat the absolute shit out of you if he heard you."
Chris: "Nah, it's okay, I have a black friend who calls me his n-gga all the time."
Joe: "You want to test out your Black Man's Blessing at this guy, then fine, go ahead."