First off Riley cooper is an idiot and deserves whatever scrutiny he gets from this incident. We should all agree on that.
Regarding the n word that ends with a, Its become a part of everyday slang amongst a bunch of people of all races in places like NYC and Los Angeles. That said while more people, especially younger heads view it as an acceptable slang word, its alot of people who don't see it that way and they have every reason to be offended by that word.
I'm white and spanish, despite hearing that word regularly on a daily basis and being referred to by that word by some friends, I just feel out of place using the word and its just not word someone of my complexion should use in my opinion.
If other people want to use it, its not my job to correct them or tell them something but they shouldn't act shocked when some black people get upset by using them using the word. Just because some people see the word as no big deal doesn't mean everyone feels that way and the views of those who get upset when they hear that word should be respected as they have valid reasons.
That said if black people, some, on an individual level, or all want to use the word then go ahead, it doesn't bother me either way.
But its funny when some white dudes are like "how come he can say it but I can't" lmao.