I don't understand why most black people are so offended by the word "Nigger"?...

Like me, I won't be offended if someone calls me a "Flip" or a "Pinoy". I also won't be offended if you call me a nigger. I knew that it is a term used by white folks to discriminate them as slaves from the time Columbus rediscovered America. But I mean, if that is really an offensive or racist word, then why do they call each other with that? Especially in their hood.... As if the word "nigger" is only exclusive to black people. If a "nigger" call a black guy a "nigger", it means "brother". If another person with a different complexion of skin call a black person a "nigger", he's insulting and a racist.