If it was observed that a noble, even a knight, permitted his captain to speak in that manner without reproach, that would indeed be considered vulgar by some.
Probably fewer than ordinary since nobles would make exceptions for anything that happened on a battlefield.
The vulgarity system works quite well. What seems to have difficulty coming across is that vulgarity is still perfectly OK so long as you don't mind being considered slightly less honorable than someone who is less vulgar than you. It's being viewed as some kind of huge black mark where all it is is that people think less of you for a short while because you said something they look down on.
Welcome to nobility and gossip.
