As a civilian, I like to think I’d treat any military officers i happened to come across with courtesy and respect. Not because they are military officers, but because they are people. 
It’s just good manners to stand up when one of your betters (social or military, the rules were defined back when officers bought their commissions) enters the room. You don’t have to snap to attention and salute him, but it’s common courtesy to at least stand up when an officer enters the room. Treat MAJ and above officers as if they were the CEO of your company, basically. Captains are middle management and LTs are jumped-up frat boys, so you can get away with more with them.
Sergeants (especially those with more than one rocker under the chevrons) are basically gods in human form, DO NOT call them “sir” (they work for a living) but otherwise show them the same respect you’d show Jesus (or your religion’s equivalent).
Civilian analogy: if you see your immediate supervisor outside work, you address them by their first name, if you bump into your boss’s boss at the bar, it’s “Mr. [lastname]” no matter what the setting.
And ofc anybody the grunts call “Top” can use first names with any officer short of two-star generals.
Not in my line of work. In pretty much every tech company I’ve worked for it first names only. Most bosses would take it poorly if you used “Mr”; it’s just not done.
True, but there isn’t any saluting while out of uniform anyway. And there is a difference from standing up and “standing at attention”
Slightly unrelated but ---- now when someone is in uniform ---- once Beloved Brother made Light Colonel any time he had to fly or go around an airport he always did it in full uniform with ribbon bars and the whole nine yards. Not because he had to; because he liked to look out for those newly minted soldiers just out of basic going home or to their first posting and proudly wearing their uniforms. They are easy to spot once you know the look. He would then sort of sneak up behind them and ask nicely “Pardon me Private, do you have a light?” At that point in their life most soldiers have rarely seen anyone over the rank of Major and that look of terror and temporary confusion at the unexpected sight of the silver (or later the chicken) really was just ---- precious is the only word I can come up with.
There is a lot of Humor in Uniform that just doesn’t translate well to Reader’s Digest. 
No there are times to salute when out of uniform. When entering a closed post the MPs always salute if one has an officer sticker on the car. I always returned their salute. It wasn’t required but not inappropriate. My wife would just sort of wave.
I was taught that you stood up, though not at attention. (Dad was in the Army, then worked for the DoD. We had any number of higher-level people at our house socially.) My father always stood when a commander or admiral or similar came into a meeting, no question. Even when he was 60, he referred to the commander or admiral as “sir”, and stood until invited to sit.
Part of what I was taught was probably to offset the natural bolshiness of a teenager, though. 
I do see my cousin (Air Force) teaching her daughter similar manners.
I’m not sure that’s a good example these days. Ours would wave, say “Hi, Jim!”, and ask if the CEO wanted a coffee. 
Hell, my boss’s boss has taken us to the bar and bought everyone shots. And he tends to wear flannel shirts and jeans to work.
IT is another world.
There is no reason that I can see for me to give a military officer any more courtesy than I would give a civilian professor. I don’t ever remember standing when any other teacher entered a room, and I went to Catholic School in the fifties and sixties.
Context counts. If you are a civilian working with military personnel at military facilities, and the officer is someone who has authority over the team, your expected response is different than if you are an employee at any regular company sitting in your office having a meeting with your employees and a visiting military officer walks in. In the military context you are expected to follow the more old-fashioned etiquette of how to behave respectfully towards an elder or someone in a position of authority. And military people are expected to use that etiquette in their behavior towards civilians when in uniform.
Out in the field outside the green zone, formalities tend to be much, much looser, because priorities.
Yeah…this. At my company, it would be insulting to the C-levels if we started calling them Mr/Ms/Mrs ____. It’s against our corporate culture.
Being fine with being on a first name basis is one thing, but to “take it poorly if you used ‘Mr’”? That’s a sign of someone who has no business being a boss. Only an idiot would see common courtesy as an insult.
I get it, though: it’s a tell of insider/outsider. In *their *field, using old-school formalities in mundane everyday situations marks you as not having internalized “the culture” and their way of thinking and loking at the world. Thus a possible liability or source of resistance.
(Though some may just be putzes for whom being called Sir/Mister implies that they are now The Man and thus a fair target for sticking it to them).
Meanwhile if working jointly with the military, or in a congressional committee, or in a Court of Law, affecting ultraegalitarian nerd-commune etiquette will be out of place.
Absolutely not. Military courtesy does not apply to civilians in any shape, form, or fashion.
You may decide as a matter of common courtesy that you will rise just because everyone else is rising (not standing at attention, just standing up). I’d do that, but I certainly wouldn’t fault you for not doing it.
I have ‘betters’? Wait, I thought we were [del]an autonomous collective[/del] a democracy.
At any rate, the idea of standing for a military officer entering the room blows my mind. I am not in the military, so we are equals. (Not that I’d know a lieutenant from a lieutenant colonel, either.) I would stand in the same situations I’d stand when a civilian entered the room.
No, it’s not a tell of insider/outsider. I’ve worked in “their field” and can tell you from experience that informality is not universal. Thinking it is shows they’re laboring under the incorrect impression that “the culture” is the same in every shop in the field.
Jebus. We’re all human beings. I’m no better than you, you’re no better than me. In other words I have no betters.
I’m guessing that the class was “military science” or the like, one of the required classes for those in ROTC. As your school was not a military school and you were a civilian, there was no requirement for you to stand. The cadets, on the other hand, were getting trained in military courtesies in addition to whatever else was in the MilSci class syllabus, so of course they were to stand at attention when a commissioned officer entered. As you noted, the officer himself or herself never mentioned it indicating that it was not out of the ordinary for you to remain seated.
Was the cadet who called “Attention on deck” in your school’s Navy ROTC?
Heh, I see a certain figure of speech touches a nerve… Remember that **Gunslinger **was making an illustration of how come the custom came to be, even with an explicit reference to the past.
FWIW, I specified our corporate culture. That is, the culture of the corporation I work at.
There are certainly high tech companies that are more formal.