It's a good question. I'd always
heard that it was a DUI if the car was running, the keys were in the ignition, etc., but I don't see it in the actual NC "Impaired Driving" law. Although it does specify that "vehicle" doesn't include a horse.
What would stop someone from asserting that a friend had driven the car to that location, and then caught a ride home from there, leaving you to sleep it off until you were fit to drive? It's unlikely, but if you're really innocent until proven guilty and they can't
prove that you actually drove the car, then how do they convict on that?