Your post #4: common sense.
Reminds me of a story I heard during my Basic Training. It seems that two troops had finished their basic, graduated, and as they were boarding the plane to their next school, thought that it was a good time to let their DI know how they felt about the eight weeks they spent in his care. This took the form of a pair of middle finger salutes. The two troops were pulled from the plane and informed that they had to do their basic all over again. As the story goes, after eight more weeks they had certainly learned proper decorum.