Well, I don't know if it's "okay" in this situation or just legally excusable, but certainly if someone is acting in a manner that gives you legitimate and justified reason to fear for your life, even if they are only saying words, then maybe.
As far as any violent response, there are plenty of things people can say that would (legally) be considered justification. I am not sure whether I really agree with the law or not on that, it's definitely still a debated topic.