I worked retail for a 2nd rate sporting goods store in a bad town. We got all sorts of characters in there. I was used to it.
One day we were busy and I was running around like mad. And older guy came up to me with a pair of shoes:
Guy: Can I get some help?
Me: Sure, what size do you need? (Assuming that's what he was looking for)
Guy: How dare you not call me sir!? I served 11 years in the military and deserve respect!
Now, sure I respect everyone, even military. But you can't just go around yelling at people like that. I usually try to throw in sir/mam when talking, but it was a mad house and I going nuts trying to serve everyone, I didn't think of it.
I just stood there for a second. Confused.
Me: What size did you say? (Making sure not to say sir)
I get his shoe and he's trying it on. During this, he starts talking to me about life, what I'll be doing in the future, etc. I think he realized how irrational he was being by yelling at me. He seemed like a nice guy when the dust settled. After the small talk and he gets his size:
Me: Have a good day, SIR.
He just smiles and says you too and walks away.
He started frequenting to the store, and I always made sure to say sir to him, and provided him with good service.
Respect is a 2 way street, and screaming at me is not respectful, no matter your occupation or what you have done.