Nonsense. I'm from North America and grew up with guns around me. For starters an AR-15 is an assault rifle which is not permitted to be carried openly. Open carry laws pertain to handguns only. Secondly, there are so many restrictions on open carry that one can get themselves into trouble very easily. The idea behind open carry is too allow for some leeway in States where guns have always been a part of daily life. However local municipal laws always override state regulated open carry laws. Basically this means that one may not carry a gun openly in an urban area if the city's bylaws forbid it, even if that state allows it.
The intent is to allow guns to be carried openly like they were in the past in rural areas. Even then, if you have an obvious threatening attitude or even hint that your are trying to be intimidating with the gun you can expect the police on your doorstep in no time. Concealed carry is another matter.
Nope it's perfectly legal in a lot of states. Probably not advisable to troll cops like that, but legal.