Is it ever appropriate to address a fellow Service Member by last name alone?

I think it's not a big deal to a extent. I mean in the enlisted force structure there is no term address member by last name only. Some people get bent out of shape over it some could care less it just depends on the person! But to answer the questions at hand, it's inappropriate to address a military member solely by there last name only.

Where respect has been earned and while two people are speaking on a professional, peer-like level, I see no problem with it so long as those participating in the discussion have no problem with it. Anyone who has any idea what military professionalism is knows exactly when it's appropriate for one person to refer to another only by their last name.

And in my opinion, leaders use last names only a bit too often.

My name is pronounced "Gunner." Being a former tanker in an Infantry Battalion you can probably imagine the nicknames that followed. My BN XO calls me "big guns" or "guns" on occasion. I don't mind it.

Me personally, I only address my peers and fellow Officers by last name. I typically address my NCOs and junior enlisted by their rank. To me it's a way to show respect for their rank and position they hold, even if they do ultimately work for me.

Peers maybe, but never subordinates, and never supervisors.

First. The Air Force IS the military. Now... In the Air Force, members of the same rank will address each other by first or last name... But most of us will NOT allow our Airmen or Jr. NCOs to address us without Rank and last name... Some of our leadership will address us by first name depending on the nature of working relationship.

In my shipboard days, all E3s and below were addressed by their last name only by everyone E4 and above. That was part of the published standard at the time (70s). There's been a one-up and one-down rule on informal addressing as well with the exception of E-7 whom you better call Chief, period, if you're E-6 and below. The officer community was a touch different in you still had one up/down but that stopped at O-5 which is the Senior Officer cutpoint vs. Major in the other services. Once out of REMFville, things loosened up a bit and nicknames were common. Down in Antarctica, everyone went by nicknames which were mostly their radio call signs. Some were rather creative. "Double Eagle" was the skipper that you could refer to but called Captain or Skipper to his face. I unfortunately had several nicknames primarily because it depended on the particular tracked vehicle traverse I was OIC on. So it was Marble One, Siple One, SAR One, whatever. I did get "Delta Alpha" One hung on me for a while due to a superior moment at the bar.

One thing I learned is perhaps due to size, necessity, or culture naming conventions are generally tighter with the Army and Air Force. Marines take it as a point of pride to state rank directly more of the time amongst peers.

It's probably more about the tone you use when you call the name.

I think that this is only appropriate to from peer to peer. If you call your subordinate by only their last name, you are saying that you are not taking the type to learn their rank. This almost makes the subordinate feel like what they have accomplished does not matter to you. You definitely should address Superiors by their rank and last name or just by their rank to show that you are giving proper respect to the rank at which they hold. It is ok to address a fellow LT or PO3 by only their last name because chances are, you went through boot camp or some type of training together.

Well that's an interesting question.

My interpretation/preference follows rank structure groupings. So NCOs can address NCOs by last name only, they can address Junior Enlisted by Last Name (since they are a lower tier) but they cannot adddress Senior NCOs by last name only because Senior NCOs are a higher tier.

Then there is the added familiarity/context issue which can further muddle the issue. Such as referring to a third party by last name in an ongoing conversation. As long as you remember to add to decorum when in the presence of those in a lower tier of ranks all should be good.

Lets put it this way, you never see it in the civilian world. Its mostly first names, never even title and last name when addressing a superior, several echelons up