Then I guess it's how you say it. If Richards had gone, rather sarcastically, "'Sup nigga? Wanna shut up and let me do my show?" it may not have been taken so badly.
The reason I found it so uncomfortable to watch was not particularly racism, but the sheer energy with which he screams the word three times.
Not the word, but the delivery.
I tend to agree. He would have slid by with that casual phrase and a smile in a comedy club although the use of the word even in that context is a little uncomfortable.. His rage, repeated use of the slur, and his reference to lynchings reflect a venomous intent. What he did was dehumanizing, and I don't give him a lot of slack because it was his stage and he's the performer and should be prepared for hecklers. This reflects on his character.
