And no, I wasn't talking about word pronunciation. I say poe-TAY-toe, you say po-TAH-toe. Or I say EYE-ther and you say EE-ther. That's variation that sometimes occurs within dialects. I was thinking more about structures of speech and how they vary. Sure, some might mock "right as rain," but it is an accepted, commonly-used phrase within one dialect group. It has a semantic meaning for that group that likely differs from how an individual from another dialect would interpret such a phrase, if s/he did not immediately dismiss it.

Just as there are accepted group understandings of "hold down the fort" or "800 lb. gorilla in the room" that will seem odd to those who think "hold the fort" or "800 lb. elephant in the room," who's to say which is privileged over another, except by conventions that often do not correlate well to general speech patterns of the various dialectal groups?