Not an entirely theoretical concept.
I'm playing once a week at what can only be described as an underground card room (although it varies in some ways from what I'd imagined an underground card room to be (small number of games, only runs four days a week primarily, although they're thinking of going to five).
So my first day there, the game hasn't started up yet, and the guy running the place(a very talkative guy, who's been making money from illicit gambling venture for years, if not decades, from what I can determine) is chatting me up and talking about the place and he brings up how secure it is (you have to go through a locked gate to get to the parking, you have to be buzzed in through two locked doors to get into the building and they have security cameras on the outside of the building, and you'd have to be insane to mess with their muscle (he's like 6-5 or something, has an advanced belt in ji-jitsu and I gather from things he's said, this is not the first discipline he's studied and, among other things he's ex military and used to body guard for Biggie Smalls (though wasn't on duty when Biggie got shot (and how many nested paranthetical asides can I put in one sentence anyway?))).
After he mentions their security this other guy, who, as it turns out has since been there everytime I've played except for one time after he was in a car wreck pulls out a semi-automatic handgun of some sort (sorry, not expert enough to recognize the make/model) and says "and if anybody does get in, I've got seventeen reasons they'll be sorry they did!"
I've never seen him flash the gun again, but I presume he carries it regularly.
Interstingly, though, this guy tends to monopolize the remote to the TV, and nobody ever says a damn thing to him about it
.