For those arguing that this 'tard's behavior IS acceptable, you need to fast forward to the present day. In the past it may have been acceptable when the majority lived on the farm or in small town America. Back then the majority of folks were familiar with and comfortable with guns and the idea of guns as tools. Like people in this forum.
Today that isn't the case. The majority live in urban environments and are not personally familiar with guns. Their exposure to guns is the "blast everything to hell" movie scenes that they see on TV and in theaters, and the sensationalism of incidents like Sandy Hook, Columbine, etc. and of course the resulting demonization of tacticool looking weapons by the mainstream media.
Those are the FACTS. Is that how it SHOULD be? NO. Is one lone numb-nutz - like the guy in this case - packing a Rambo looking rifle around the mall - going to make John-Q public more familiar and comfortable with the sight of guns? NO IT ISN'T. Is it gong to disturb a lot of people? DAMN RIGHT IT IS. Like I said, it would disturb me. If I saw a guy walking around packing an AR in public, I'd have my hand on my CCW and be eyeballing him pretty darned close. I'd also be getting me and mine the heck away from the situation ASAP.
If the fool was just walking to or from the gun store by the shortest route, and being less blatant about displaying it then there would have been no problem. BUT HE WASN'T. He was walking around from shop to shop with it slung over his shoulder dressed like some sort of commando. Why did people get upset? Because there are only two possible reasons for doing that. Either you're trying to provoke a reaction, or you have murderous intent. If he was trying to provoke a reaction, he succeeded. On the off chance that his intentions were to shoot up the place, calling the police is not an unreasonable response - especially buy Joe or Jane Average who don't know spit about firearms. Familar with the idea of better safe than sorry?
Suppose he had been a nut job, and was allowed to walk around like that for a half hour or so before suddenly starting to spray lead? Every person who ignored him and DIDN'T call the police would feel like an idiot, and even feel partially responsible for having done nothing.
TECHNICALLY carrying the rifle around wasn't illegal. WHEN and WHERE he did it was disturbing the peace. Like I said, the only two reasons for doing what he did are to be in-your-face about a 2nd amendment issue, or to do something horrific.
Despite the fact that WE feel like it SHOULDN'T be that way, the fact is, that is the way it is. Like it or not, carrying a tacticool rifle in a public place is NOT the socially accepted norm. Doing it anyway does NOT further our cause. It makes all those who are already afraid of guns view us as inconsiderate, unreasonable, and even irrational. This guy and people like him don't help us, even if you somehow can't see anything wrong with what he did, it still hurts our cause.