If someone has directed to this page, it's likely because you used a non-standard abbreviation of South Carolina that has caused a Gamecock fan to feel offended. You're not completely at blame here. South Carolina fans are rather unique in their insistence upon being referred to using only a specific set of pre-approved shorthand.
You see, in The Great Brand Wars of the 20th century, much of America collectively decided that both of the most logical abbreviations -- USC and Carolina -- were the province of other schools. Gamecock fans are pretty sore about this.
Still, within the state of South Carolina, both "USC" and "Carolina" are immediately and reflexively understood as references to the University of South Carolina. If you never left the state or watched ESPN, it might never occur to you that there are English-speaking people to whom these words mean something completely different.
Is it our preference that you adopt the same standard of abbreviation as the locals? Yes. But most reasonable Gamecock fans understand that someone in Chicago, to pick a city that I live in, asking an office mate, "What do you think of Carolina's chances this year?" will, at best, be greeted with a look of uncertainty as to which school is being asked about. (We all know this very famous look.)
So what am I allowed to call you people?
As someone who frequently writes about South Carolina, I understand that repeatedly referring to South Carolina as South Carolina gets repetitive. And in some settings, character limits require a shorter term that is also precise enough to be understood by a geographically diverse audience.
In the vast majority of contexts, though, USC and Carolina are going to be just fine. Let's say you're writing an article with the headline "South Carolina wallops Georgia, 52-0." If the body of the text contains the sentence "The game was essentially over when USC tailback Mike Davis plunged into the end zone to push the Gamecocks' lead to 21-0," do you know what absolutely no one is going to think?
HUNH? When did the USC Trojans change their mascot to the Gamecocks? And when did they tag out South Carolina (is that even legal?) in this game that I previously understood as a contest between Georgia and South Carolina, not Georgia and USC. Is Mike Davis even eligible to play, having apparently transferred from South Carolina to USC? Or is it the Mike Davis who used to play for Texas? Or the other Mike Davis who was a running back for South Carolina from 2005-08?
But there are situations in which there are not enough context clues to make it clear which USC or Carolina is being discussed. Consider the following hypothetical tweet:
@philsteele042: imo usc is v underrated. 4 me they're a sleeper pick to make the cfb playoff.
No matter which USC he's talking about, this is only going to create confusion and require Phil to issue a follow-up tweet clarifying his statement. In such a scenario, either S.C. (the AP-style abbreviation of the state) or SC (the postal abbreviation of the state) are acceptable. I often rely upon these very abbreviations on Twitter. They're lifesavers.
ESPN occasionally uses SCAR and S. Carolina. I don't think anyone is necessarily going to get mad about you writing either of those, but it's a weird look. (You just pictured an evil cartoon lion, didn't you? See my point?)
What should I absolutely avoid?
USCe and USC, Jr. are the two abbreviations most likely to draw the ire of Gamecock fans. Of course, USCe suggests that we are the USC of the east -- perhaps a satellite campus of some sort. USC, Jr. suggests a diminutive version of Southern Cal (its son?). My anecdotal experience is that those using the latter term are almost always attempting to wound our pride. In the case of USCe, I've seen it used on several occasions where it seems pretty clear -- from the text itself or from follow-up conversations with the author -- that no harm was intended.
Whether or not you intend it as such, we perceive these terms as putdowns. It makes us feel as though the school that comprises so much of our identity is not being acknowledged as an independent entity. Instead, we are defined by way of comparison to another school -- in this particular case, being less than another school.
If you've been using these without intending offense, we can still be friends. You didn't know any better. Now you do.
Am I free to disregard all of this?
Of course. But if you say "Hey, Eric" to someone at work and he responds "Actually, my name is Dave" but you keep calling him Eric, then you're kind of an asshole.
DO: South Carolina, Carolina, USC, SC, S.C.
FINE BUT WEIRD: S. Carolina, SCAR
DON'T: USCe; USC, Jr.
All of the above is, of course, my opinion. I happen to think it's fairly representative of how most Gamecock fans feel about this topic. But if you think I'm dead wrong or left out a popular abbreviation, be sure to let me know in the comments!