What people need to understand is that this woman deliberately used a word that was used by white people to describe black people during a time when they were considered less than human.
Does that mean it's a good thing to respond the way this man chose to? No, but if you think this is indicative of the way he handles insults or situations in general, you're severely misunderstanding the impact of the slur in question.
And part of the reason black people can feel compelled to respond this way is because they feel like there isn't much other choice. While we have hate crime laws in place, that doesn't change the fact that many people still just think of the slur as "any old insult" that should just be ignored. When in reality, it's a truly vile term that dehumanizes the person being insulted based on their race.
This doesn't justify violence, but we need to understand why the term inspires the reaction it does. Because outside of the few people who are simply ignorant of their own behavior, racists aren't likely to change their behavior because it upsets the group they are racist against. Instead, we need to make sure that people feel like they have a course of action they can take that will at the very least allow them to extricate themselves from the hateful situation.
There are at least 5 people here who literally don't care about any of that. 2 of them have me blocked, but that doesn't change the fact that that they have demonstrated that they don't care. It's all about "yay! This gives me an excuse to be incredibly racist in such a way that encourages others like me to be the same! And we'll just deny it and make excuses!" ---