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 know when I was with the 11th ADA Bde the Colonel called my Bn Co "Jimmy"!

No such regulation exists.

No such regulation exist.

AR 3825-968...

My am CW3 Young....Chief is my first name.....period

When I was in USASOC it was a lot of first names. But even as an officer I never assumed the privilege with the NCOs unless I knew them and only in very specific situations

Seriously? Hey if you don’t like it simply bring it to their attention in a professional and respectful manner. Then live with the results

As far as I know, there isn't one. I've only heard it done by the Air Force, but that was also only in jest.

No. They should be addressed by their rank and last name.

AR 600-100