As a college freshman many years ago, I took a class that was taught by a uniformed USAF officer - a Major, I think. He was in uniform when teaching the class, and the ROTC students in attendance were also in uniform. When the instructor entered the room at the beginning of each class, one of the ROTC students would call out “attention on deck”, and they would all jump to attention and become silent until the instructor called “at ease.”
I was not in the ROTC. Being a civilian (the only one in the class, IIRC), I did not feel compelled to follow suit, so I remained conspicuously seated each time this happened. The instructor never made any mention of it. It felt a bit awkward being the only one not standing at attention, but at the time that awkwardness made me feel even more stubborn about it, so my behavior persisted until the end of the term.
Was I out of line? Is there some code of etiquette under which civilians are expected to stand at attention the same as junior officers when a senior officer enters the room? If so, is there any rank to which civilians are senior and therefore don’t need to snap to attention (or simply stand up)?