In all honesty: Talk with your manager. They probably already know all this, and want to find an excuse to give them a talk.
Working at the desk, I've had a person who was a control freak who was transferred over to our store. Was the same "rank" as the rest of her coworkers, but barked orders, assumed you didn't know how to do your job, and talked condescendingly to the rest of the staff. I talked with my manager, and he told me that I was definitely not the first one to make a complaint. As soon as the next day, she stopped talking altogether.
But for fun, let's run it down by your man's rules. Let's critique and talk shit behind his back.
Regarding the coupon thing, interject, save the order, and take it to your terminal and do it by the book. Apologize if necessary. Dude will get pissed, don't care. Make it right for the customer, and let him complain all he wants. He wants to prevent people from using coupons as it's part of some weird control complex he has. Remember: He's a 40 year old grumpy dude working part-time at the CS desk.
If he's talking shit about people, best to ignore it. People talk behind each other's backs, even the tight-knit group of co-workers turned friends I have that work at the desk. But more importantly, I doubt you are the only one who thinks he's an ass, and probably ignore what he says as well. He talks about other people because he's insecure, and isn't interesting enough to talk about things that aren't other people's misgivings. So just remember: He's a 40 year old grumpy dude working part-time at the CS desk.
He can't take criticism because he refuses to learn. He's been doing this forever, he hasn't motivated himself to do better, so this is the small ledge he's heralding himself on. The best kind of leader is one that continues to learn from others, and accept that they make mistakes. But he will refuse to do this, and for the remainder for his career at Publix: He's a 40 year old grumpy dude working part-time at the CS desk.
So whenever he's giving you a hard time, repeat that phrase in your head. Remember that he has no control over your life, and that you are the better person. Be the best you can be, no matter what you are doing.