Your entire point seems to boil down to " But i am pissed, i can't just not be pissed, that takes so much effort." , and really that is a horribly poor line of logic, and you then take the step of saying this would cause you fear, not only that, but enough fear that you wouldn't trust this person for the amount of time it takes to walk to your door and close it.
Nice strawman, can I keep it? It'll look nice on my shelf of other useless brick-a-brak. I never indicated that I, personally, would feel either fear or anger, but merely indicated that those would be normal under the circumstance. That you claim "you then take the step of saying this would cause you fear", is clearly disingenuous, and you should be ashamed of yourself. Being accosted on the street by some puffed-up twit is sufficient cause for caution, which is what I mean by not turning my back on him. It would be foolish to assume that continuing about my way, without dealing with him, unless I were at my very doorstep, is the wisest course.
I have to say, that sounds very paranoid, and that is coming from a guy that does walk around armed, on a constant basis. Letting your emotions run your life, let alone feeling justified in this, is how crap like this happens. If the first gent were to simply say to himself "I'll just give the baby his bottle and tell him what i am up to, and if he wants to go further, i'll just outsmart him." he'd be alive today. The knob in question wasn't a sociopath, just a jerk with the same fantasy most jerks have, being dirty harry.
Paranoid? Ridiculous. It isn't paranoid to respond negatively to harassment. Why is it that you feel the need to "walk around armed"? Is that not due to paranoia? I see no reason that anyone should feel that need, apart from unreasoning fear.
I have a suspicion that your story about what the "correct" response should be, isn't how it would play out for you in real life. After all, you feel some need to be armed, eh?
And escalate is a perfectly appropriate word, you know how this person is going to react, and that by giving your answer that you admit is simply emotion fueled, it is going to simply cause him to act more like a knob , than by relating very simple information, that is not going to harm you. He isn't asking for a credit card number, or who you were banging, hell, you don't even have to tell the guy the truth, just make some crap up as to where you went.
You really ought to take a moment to look up the word
escalate. What makes you think that you, or anyone else, is going to know how this person will react? I certainly never said anything about my reaction being emotionally fueled, that's simply your inference, and again, you
don't know what his reaction will be, nor does he deserve an answer to his questioning of your presence, and certainly not a conciliatory one. Personally, I find that being truthful and honest is more likely to prevent escalation, than trying to lie your way out. I'm not at all violent by nature, and have had to learn the hard way that people who have no compunction about accosting strangers the way that Zimmerman likely did, won't quit easily, as their intent is to start trouble, and not otherwise.
Literally the only option that is guaranteed to make the situation more of a confrontation, is the emotion fueled snark of " None of your business." indeed it is none of his business, so lie. If your really that scared of telling someone you went on a snack run , it is the easiest way to not give that ultra valuable information, and not end up in a crappier situation than when you started.
Your assumption that "none of your business" must be emotionally fueled, and a snark, is preposterous on the face of it. The rest of what you say here, to lie just to satisfy some impudent nit, describes the poor habit of dishonesty, and is likely to only lead to further impudence on the part of the interloper.
I have no small acquaintance with these situations, and have learned by trial and error how to avoid escalation. Presenting oneself as a milquetoast only validates the view that you may be trifled with.