Born in the south and moved to Philadelphia in my early twenties. It was more culture shock than some other countries I’ve been to. Folks in Philly don’t hold back. If they don’t like you they tell you, to your face. They also don’t feel the need to add all the extra and often unnecessary pleasantries to every social interaction. Honestly for a “well mannered” southern kid it was pretty liberating to get to drop all that.
It took me a while to figure out. Like I knew Southerners can be mean and judgy, but I didn't think about how until I traveled to other places and saw how much more straightforward people are. It's nice when kindness is kindness and there's no underlying meaning.
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."