Many, many years ago I managed a convenience store. Early one morning a nicely dressed professional looking woman came in for coffee and she was the only customer in the store at the time. She poured her coffee and put in one of those individual creamers but the creamer curdled. She was quite upset and showed it to me and I of course apologized profusely and told her that I’d go to the back and get a fresh box of creamers which I did. FWIW, sometimes one out of a hundred of those will curdle for no apparent reason. I returned and got her a new cup, even poured her coffee for her and then handed her a creamer from the newly opened box.
What she did next will never cease to amaze me. She looked at the cup, picked it up, glared at me and then told me “I don’t want any of your G-D coffee” and then she hurled the cup of scalding hot coffee at my head. Fortunately I had some pretty quick reflexes back then and ducked but the scalding hot coffee still hit me although not in my face.
I was so shocked that I stood there frozen as she stormed out of the store, got into her very late model and expensive car (a BMW IIRC) and sped away. If I had more of a presence of mind, I might have gotten her license plate number and called the police to file assault charges against her but then again there were no witnesses and we didn’t have security cameras back then. And this wasn’t the first time I had been horrifically verbally assaulted by an angry customer for no legitimate reason or the last, although this was the only time I had been physically assaulted with hot coffee, which BTW is a lot more dangerous and potentially physically harmful than a bag of popcorn.
So what if I had had a firearm on me that day? Would I have been justified to pull it out and shoot her in her back as she was leaving my store after she assaulted me? Would I have been justified to run out after her, get in front of her vehicle and threaten to shoot her or shoot her if she still tried to speed away?
What about the guy who severely and very aggressively tailgated me for well over 10 miles on a narrow country road a few weeks ago and once he got in front of me, kept slamming on his brakes in hopes of causing me to hit him? What he was doing IMO was a lot more dangerous and potentially life threatening to me and to other drivers on the road that day than some guy throwing some popcorn in someone’s face. Would I or should I have been justified to follow him, pull out my gun and shoot him? What I did was to take out my cell phone and take a picture of his car and license plate and I called the police, not that he was caught or that anything happened. FWIW, here in PA, what I did, using my cell phone while driving to either take his picture or to call the police, is technically illegal as the cop who took my report reminded me.
Your tailgater is a different matter. You would not be justified in following him, however his behavior would put him at risk if he were to attempt to approach you.
For example, if you pulled over to make the call and he pulled over in front of you and aggressively approached your car. The car with windows closed makes for pretty good protection. If he brought a tire iron with him and took a swing at your window, you fire. There won't be time to figure out how quickly he can break the window and get to your head and you shouldn't have to make that calculation.
If the guy, instead of a tire iron, brings a bag of popcorn and throws it at you through the open window, then you get to try to figure out what he is going to do next and you may have to do it while somewhat blinded by popcorn and salt.
She probably shoplifted something while you were in the back getting more creamer and was upset at you because you came back too soon.