As I was leaving out the door, I held it open for a guy and he looked at me and said "You can't bring a gun into a bank."
I said "I didn't see a sign on their door saying they prohibited guns."
He then said "It's a federal law."
So, is he right or is he full of crap.
He is wrong. I met a liquor store owner who said, "No, you're not allowed to carry a gun in a liquor store. I know." That liquor store owner was just as wrong as the guy for whom you held open the door.
In response to his "you can't bring a gun into a bank," I would simply have said, "Open carry in the State of Colorado is lawful under both state and federal laws."
Don't give others the option for arguing points they think they know. It pays to know the law and be the authority.
I recently had a very polite conversation with a police officer. It was "very polite" because I've learned to keep it that way while maintaining the upper hand, at least with people who are even the tiniest bit open to the fact that they may very well be wrong.