One big difference I've noticed: Well mannered Northerners do not often say Ma'am or Sir, unless they're being snarky or work in the hospitality or food service industry (and even there it'snot all the time). I have rarely met a Northern child that ends a sentence addressed to an adult with Ma'am or Sir.. It sounds almost sarcastic from a Northernkid because it is hardly heard.. Or indicates a very strict upbringing. They are way more likely to call an adult by their first name, even. If a Southern kid tried that, whew. I've known some Southern children, teenage and adult, who always address their parents as Ma'am or Sir.

As you mentioned, there's no direct insulting to the face, at least none that I've encountered. But there sure are a lot of faux kind comments like "Bless his heart."

ETA: I edited this comment a bit upon reflection.