When I'm open carrying I realize that I may (again!) have issues with LEO's. Most of the time if you know your rights and the law you will be fine. But you're right, if you had stood up for yourself you probably would have pissed him off and he would have hit you with everything he could.
Without sounding condescending you need to learn the laws and make sure you're not breaking any non firearm related laws while oc'ing. If you had a holstered firearm you are clearly not guilty of GATTTOTP. You don't need to talk to a lawyer to ascertain the legality of OC in NC, or read anecdotal references to laws on pro gun sites. You may find the links on these sites to NC statutes and legal precedence helpful though.
Sounds like another cop bent on monopoly of force. Not everyone wants to go through the hassle and expense of getting a concealed carry permit, and many would rather OC for various reasons. Cops will eventually get more used to it when we stand up for our rights and fight against oppressive cops who don't know the laws they're paid to enforce.