It depends on where you live. In some states open carry is legal. In Missouri, for example, there is no state law forbidding open carry. There is also not lawful to carry concealed, so if one carries, it must be open. There are only two things that cities and local juridictions can do beyond state law in MO, open carry and firing in city limits. In otherwords, cities or towns can prohibit open carry if they wish, but state law doesn't allow them to come up with their own restrictions beyond state law.
There are a couple of problems with this though. Finding state laws isn't too difficult. There is no list of what cities and towns ban open carry and it is difficult to find out which ones do. Calling the police or sheriff doesn't always give the right answers. They will often say "you can't do that", but cannot tell you what city code it violates or give any kind of reference. I asked my sheriff's department and was told to look on the internet. Well, I didn't find anything concerning that. My guess is that wouldn't hold up in court. Even if one does open carry where is is not illegal, my guess is it might attract a lot of negative attention and perhaps invite harrasment. So, if you carry concealed where it is not legal, you could get in trouble, although no one would know about it if it was truly hidden, or you could get in trouble for carrying openly and obeying the law or not knowing the law.
Sure is strange, if you go to traffic court and say "I didn't know", the judge will say "the law is the law......", but if the president does the same (and obviously lying when he does), its okay.