Whether most people have heard it or not isn't the point.
The fact is the guy is an idiot. Calls CC a slur. CC asks him what he said. Guy repeats the slur. Idiot. He thought he was being slick by using a term most people wouldn't know. Idiot.
Wonder how he'd feel if CC called an officer by a 3 letter derogatory term...
It'll happen someday. People have gotten close (Gwynn, Brett, etc). No reason it couldn't happen. I think all the scouting will make it less likely, but it'll happen eventually.