I would leave immediately, noting as much as I can describing the individual. Then a phone call to 911 to report a man with a gun in a restaurant. Let the police sort it out. It’s their job. Not mine. Not the restaurant manager.
It’s been my experience that those who legally carry do so in a respectable manner, and strenuously avoid any perception otherwise. Taking the OP at face value (because we have nothing else to go on), the guy is a jerk.
Too coy or just exceeding the attention span of respondents when combined with the the whole rest of the story, since almost every response has ignored it.
I assumed it might mean NY or NJ but I don’t know offhand if carry permits are quite as rare in NYS outside the City as they are in the City and NJ. In the City or NJ a person carrying a gun in plainclothes is almost 100% likely to be a cop or a criminal, give or take a few connected celebrities in tony parts of Manhattan. 
And carrying it improperly tilts it away from cop, though doesn’t rule it out. I’m not sure offhand whether that’s equally true in upstate NY.
I did miss the “Bloomberg” part, so I apologize.
I was thinking of one of the 30+ states that do have reciprocity and rather similar laws regarding CCH. In my state, there are hundreds of thousands of CCH permit holders. We’re sort of in the middle…hardly ever see open carry, but it’s pretty likely you’re within a couple hundred feet of a legally-carried gun whenever you go out in public.
This has been nagging at me a bit.
I AM sorry I didn’t leave immediately.
I’m sorry I didn’t tell my kid “oh shit, our cars on fire!” and drag him the hell out of there.
Or:
“HEY YOU IN THE BLUE JACKET! YEAH, YOU!
DID YOU KNOW YOUR GUN IS ABOUT TO FALL OUT OF YOUR POCKET?!!!”
Looking back at the thread, in post 27, he also said:
Which also points to it being upstate New York.
Though I have a concealed handgun license, I “open carry” 90% of the time. My gun is always secured in a holster.
If I witnessed what the OP saw, I’m not sure what I would do. I suppose if I lived in a state where carrying a gun was routine (e.g. Ohio), and the person didn’t look… unstable, I would probably say something to him. “Dude, I’m glad you’re carrying. But you really need to secure it in a holster. You are being unsafe to yourself and others.”
I think telling the manager was the right thing to do, but I admit to bias on this subject. Guns make me very nervous unless they’re in the hands of the police.
Chances are he didn’t realize that it was printing or protruding from the pocket. I would have very subtly gotten the person’s attention and indicated that their gun was exposed. That’s what I would expect from anybody if that were the case with me. I’ve done it myself for other people. But, barring that, having the manager do it for you if you’re overly concerned about it is fine too.
Eh, I don’t see a problem with telling the manager. I suspect the reason he responded weirdly is because by the time you told him, as you said, the guy was getting in his vehicle and leaving. At that point the manager can’t do much, he’s not going to chase him down and grab his plate number, most likely. So he was probably pretty confused/unsure of what you were expecting. But there’s some small chance the manager commits the knowledge to memory and “keeps an eye out” if the guy comes back, and then maybe calls the police if he notices the guy in the restaurant some time in the future with a gun.
This. The guy might come back.
If you were the restaurant manager, wouldn’t you want to know about this?
Also, if later the guy did come back and shoot up the place, the OP would not be able to forgive himself.
This is one of those times when I make the decision based on my assessment of the magnitude of the potential consequences of doing something v. doing nothing.
Disagree. I would call it prudent. A gun being carried loosely in a pocket is unsafe. It should properly be carried in a holster. If he doesn’t know how to carry it safely, chances are he doesn’t follow other safety practices. There is a good chance he could accidentally shoot someone. Whether he can legally carry a concealed weapon isn’t an issue. I’m sure the majority of gun owners do practice good safety procedures when carrying, but it just takes one doofus to spoil things for others. I’m sure the local or state police would be very interested in someone who is handling a gun carelessly.