In the business I'm in, I speak with folks all over the country, many of whom are extremely pompous. Some folks are quite nice about my southern accent, but some folks are so taken back, they can't mask their rudeness over it.
I've found that if I become quiet after an affront and let the silence fall like a rock, they get the hint.
There is no excuse for being rude, especially over something like an accent.
I don't think I sound southern, but I've lived in VA for over 20 years so I guess I picked up the accent. When I visit my Dad in NJ, I always get weird looks from people when I talk to them. Especially if I say "ya'll".