I guess reasonable was the wrong word, as I was not referring to the 'reasonable person' standard.
Yup, not referring to the test/standard, I am referring to what I would personally find threatening. I consider myself to be reasonable, which is why I used that word, but did not realize this was a reference to a specific concept. However, and regardless of what should be morally or legally correct, if I am feeling threatened and there is a legitimate reason for it based on another's actions, I will respond. Now, if you include the law, my standard for what constitutes as a threat will likely rise so I don't get in legal trouble, but I see that as a problem rather than a benefit, since it's adding an extra fear that gets in the way of my judgment.
This is something specifically for me in response to absence of law, and I don't think there should be a law/legal edict based on it because while I consider myself reasonable/clear-headed/just, I would not consider many others to be the same, and I'm sure people have a different opinion of me.