Anyone know what Army Regulation (or any branch) that allows a higher-ranking officer to call a lower-ranking officers by their first name?

I was a deputy sheriff for several years earlier in my life and I used to say the sheriff and I were on a first name basis. He called me Mike and I called him Sheriff.

I'll probably draw a little fire from the Officers for this, but I always found it unprofessional.

I would say it is better suited for peer to peer.

Respect. My battalion commander called me Craig or chief.

It's not regulatory, but it it is a cultural norm, a tradition among officers.

There is no reg that I am aware of. It has, I suspect, always just been "tradition". A LTC I used to work for always called me "Fin" (I was her OPS NCOIC) and it just never bothered me.

I think that this has its place depending on the setting and climate of the particular office you’re working in. When in the s3 shop there all the officers called their peers and subordinates by their first name, and nearly everyone, enlisted or officer, had nicknames we would answer to in the shop. If we were outside the office or had visitors it tightened up. When I was in the s3 at 2-7 IN at Stewart everyone was addressed by rank and last name. It was just the atmosphere that was instilled and we all followed.

Calling a subordinate by their first name is a term of endearment and the sign of a caring leader. It is often used with a sarcastic tone but it is a sign of love and respect. A good leader knows about and cares about his/her subordinates as individuals. Calling them by their first name shows that the leader is recognizing the individual.

As a former Special Agent, it’s the norm when we’re on investigative status in our field office in civilian clothes.

Air Force allows it and is documented in AFH36-2618 para 3.1 ....." Each rank includes an official abbreviation and term of address,
however Airmen senior or equivalent to the member may use first names and/or call signs"