I never salute officers in the field, and when they get mad, I just remind them that if this was a combat enviorment they would be marked as a target. He if you want a 7.62x39 round in the Grape then be my guest....sir. But all of the really good officers don't salute in the field.
Saluting in civilian clothes though? I do believe that you are not supposed to. You are only supposed to recognize the officer, and give the the proper greeting of the day.
It is always funny seeing new LTs get saluted, they look so happy when you salute them.
Some officers avoid large groups of enlisted men just so they don't have to salute. We had one such officer, 2LT Hastings(bigtime *******) an FA officer. We knew he hating always giving out salutes so, we were walking in a gaggle, and when we saw him walking towards us, we all merged into one single file line, and spread out about 5-10 meters apart, just so he had to return ALL of our salutes.