I find that people with bad manners who rant against RKBA in public do more to help our cause than they might ever imagine. The target (pun intended) audience just isn't drinking the Kool-Aid anymore.
I tend to smile and laugh at them while continuing with what I was doing - frustrates them in no small way
As to the legal question, unless there is actually a physical threat, I don't know of any law that would apply. The property owner can ask the offender to leave of course - disturbing the peace might be a consideration.