When I was working as a contractor in EUCOM, my primary contact was a Lieutenant Colonel. It was years ago, and I can't remember now how, exactly, I addressed him. But I do remember at one point wondering to myself if it was rude for me to use the full modifier for his rank, and whether I should address him as "Lieutenant Colonel Smith" or if just calling him, informally, "Colonel Smith" was acceptable and/or appropriate. I don't imagine, for instance, anyone bothers calling a Second Lieutenant "Second Lieutenant Smith" when referring to him casually. And I sincerely doubt anyone addresses a Brigadier General with his full title. I had to work with an Admiral for a while who was an O8, and I didn't fucking call him "Rear Admiral." For the life of me, now, I can't remember what the fuck I called him. Which is bizarre, because I worked with him for about a year.