The vast majority of people don't go around showing off weapons. In fact, threatening someone with a gun is usually a crime in and of itself - you might be allowed to CARRY the weapon, but you should only pull it when you expect to need it. Using it to threaten someone is, in most jurisdictions, illegal unless you can prove you needed to do so in self-defense, and for that to stick, you need to be in a situation where it would have been legal to shoot.
That said, every now and then you'll see some whackjob carrying their rifles with them as they shop, but that's them pretending they're badasses fighting The (Black) Man (In The White House). Everyone I know who actually carries for a sensible reason either has a CPL (concealed pistol license) (2 people) or uses a visible holster (1 person) for their pistol. (I'm not counting people who carry as part of their jobs, such as police, but they generally fall into the second category). None of them take their ARs shopping with them.
The truth is that the people hauling their rifles with them as they shop are doing two things: trying to intimidate gun control advocates, and showing which people need to be shot first if there's a violent robbery. (Really happened - someone was trying to rob a Sam's Club, and some open carry advocate grabbed his rifle and started angling for a shot. The robber's backup pulled her pistol, walked up behind him, and blew his head off.)
If I were going to rob a store, didn't mind killing people, and saw a few folks carrying their rifles, believe me I'd just find a position where I could take them all out while they're still trying to figure out what's going on and/or trying to pull the rifles off their backs. It doesn't help them that the typical civilian reaction in a spot like that is to freeze, and it doesn't take but a couple seconds to shoot them all while they're still going "Huh?".
And for the record, the one time I got robbed, they used a baseball bat, not a gun.
Anyway, you may see more of the gun-waving and gun threats if you hang out with gangs or drug runners a lot, and if you go shopping at Wal-Mart, especially in deeply-conservative areas (as they're the always the ones shopping with assault rifles). Otherwise, you're very very unlikely to ever see a gun pulled for any reason. It really isn't like in the movies.