the N-word

Race issues seem to come up a lot in my daily life because of where i was born and who I am around most of my life. I am used to being surrounded by blacks, Latinos, and Asians in inner city settings. One of the biggest issues that comes up is the use of the N-word. Honestly, most people have wack ideas of the appropriateness or inappropriateness of the word. The people I respect are those who deem it inappropriate for all or appropriate for all.
I just don't get it when black people just throw around the word all day long, use it about and direct it towards white people and then get really mad if a white person even thinks about using it. Now, I'm not ignorant, I know that the N-word has extremely negative connotations and has been used by whites very wrongly in the past. I just don't get why the black population seems to want to keep the term in circulation so bad. Even more so, I don't get why the black population will use it right to their white friends faces, but then get really angry when their white friends use it back in a completely amicable way? When a black person has a white friend or girlfriend or wife and he calls her the n-word in a joking, kind context, why is it a mortal sin for her to do the same? It just seems inconsistent. To me, if you use it with some, you should allow them to use it with you. And if it offends you so much when you hear some people say it, you shouldn't be cool with furthering its use yourself.