MPR had a segment this morning with Kerri Miller speaking with Anatoly Liberman on The Daily Circuit about differences between British English and American English. It was fascinating, and I recommend looking it up and replaying it.
In the process they got into regionalisms and how in the UK it means folks from the north and south can't understand each other, while in the US it just means an accent. While that may be true here on the whole, I got a lesson or two back in about 1980 that shows it's not universal.
I had a coworker for a bit who was a local - as opposed to my neighbors who were all northern imports. While I can't recall her name, I do remember the conversations. There are two particular words with completely opposite usage between Minnesota and rural Georgia: nasty and ugly. Here, ugly refers to appearance and nasty refers to behavior. There, ugly refers to behavior and nasty refers to appearance. If your kid in Georgia is a brat, you tell them not to be ugly. If your clothes are worn and dirty, they're nasty. But even though the words are opposite, the meanings are plain.
She was also helpful in teaching a Yankee the proper use of "y'all" and "all y'all", and though she tried to instill the various kinds of "yonder", I was hopelessly lost. I have no clue where up yonder, down yonder, and over yonder are. She was quite the colorful character, and one phrase I will never forget. She had several male acquaintances she didn't think very highly of, and had a phrase for putting down (never to their face!) those least worthy, though I never got the impression it came from personal knowledge. It was just a cutting insult: Needle Dick.