Who is "allowed" to say the "N" word?

I was on Facebook the other night, and I was reading through some of my friends posts. The issue with using the "N" word is very controversial and according to some of my friends on Facebook they were discussing who is allowed to "use" it. I hear this word thrown around with a lot of my friends who are mostly black. They refer to each other as this word mostly, and I suppose some of the white friends that they hang around whom they consider "black". I saw from one of my friends post's that the only white person allowed to say the "N" word was a guy named Josh, and that every other white person shouldn't attempt to say the "N" word. In any case calling each other the "N" word during discussion shouldn't be tossed around as lightly as it is. A lot of friends that I know who are black get very offended when a white person uses the "N" word. When I have heard people throw around this word it seemed very disrespectful for me to hear. Whether or not some people think it is or isn't depends on their knowledge of the term. Many African Americans take offense to white people using this word. Unless an African American friend has used the term with them do they only feel it to be okay to say around them. After reading this post online it just made me question, is it okay for any of us to use the "N" word even if he or she is African American, or should none of us use it at all?