Doesn't SC means something different depending where you are at the time of it's use? If you are in Arizona and say SC it means Southern Cal but if you are in Durham it means that other Carolina.
This whole discussion is just something you have to let people get out of their system.
You have to be conscious of the fact that this is new ground or at least infrequently trod ground for some folks. We of course have heard it 15,000 times.
If we're in Raleigh, we know that saying Carolina is going to draw comments or confusion. If we're out of the Southeast, we know that USC might be genuinely confusing. But for the most part, we don't have any trouble with people understanding who we're talking about. Mostly, it is people doing a very old comedy routine.
Sort of like the whole 'Cocks thing.