Chances are that you’re dealing with a gentleman of the Old School. He may address all men as ‘sir’. On the other hand, may be forcing himself to be polite in order to restrain himself from issuing you the beatdown that you deserve.
There’s one way to find out. Say this. “Excuse me sir, but I was not raised to be a gentleman and quite frankly I’m embarrassed that you think I might be one. I am just a dude with no home training. I literally had to go online to get some education about this. Most people of my generation don’t understand the ways and means of etiquette. I appreciate your manners, but I honestly don’t know how all that works.” Or something to that effect.
If you ARE dealing with a gentleman, he will smile thank you for your honesty. He will then decide whether or not to indulge your ignorance, which would be something of an actual mark on your character, in which you instantly become ‘stupid white boy with no home training who thinks I’m one of his little friends’ in the back of his mind. This thus becomes a mark on his character as well. Why should he change his ways just because you are uncomfortable with a term of mutual respect, straying from the path of a gentleman as he was instructed as a young man? Your best case scenario here is that he offers a hand of friendship. If he does, then he would address you by your first name and then he would be obliged to allow you to call him by his first name. But he would be within his right to decline such a personal friendship depending upon the context of your meeting.
Understand that the formality of ‘sir’ allows you both to keep a respectful distance. I would recommend that this is a distance you should accept until such time as you are invited to a more intimate friendship.
I assure you that if he calls you sir again, even if he has kicked your ass to the floor in the back of his mind, you’re dealing with an actual gentleman and there’s nothing you can possibly do about it.
If you are NOT dealing with a gentleman, you will have the advantage of this understanding of how a gentleman would comport himself formally plus the benefit of reading his mind as I have provided an example. You then have the slight advantage of behaving like a gentleman yourself in case he laughs in your face. He’ll call you Jimmy or whatever you like, but he won’t offer his own first name. He may even say, OK Jimmy, you can call me Mr. Franklin. Now you’ve lost face. Do you care? I think you should.
You see, in the face of arbitrary hostility and in situations where anything at all might happen the only thing you have to save your body and soul are formal manners. You need only consider the recent controversies over ‘open carry’ of firearms. If everyone carries firearms openly, how do you express your intent not to fire unnecessarily? With manners of course. When you get a chance, watch the movie ‘Winchester 73’ starring Jimmy Stewart, speaking of firearms. Well, if words can kill, then manners are the proper holsters.
Here’s the TLDR. Imagine your dear old grandfather from the Old Country. Why back then they used to call him ‘boy’, even as a full grown man. All he ever wanted was to be treated with respect, like everybody else. He was certainly willing to do his part. Oh but these young people today. They want to be called ‘boy’. They don’t want to wear a shirt, a tie, polished shoes. Ah what do they know about respect?