Propriety, or being proper, speaks of conforming to accepted standards, in bahaviour or morality. As in polite, and nice.
As you may have gathered, I do not care much for strict or stringent propriety. Not that I'm opposed to having good manners. But trapped in the obfuscation of political correctness, for example, we lose a sense of what is real. We use "proper" language to hide meanings and motives, actions and attitudes. It's phoney baloney (as Mel Brooks might say).
I think we, collectively, as Humans (particularly North American Humans) tend to spend much too much time and energy on propriety. I think plainer speech, without being unkind, would help all of us.
P is also for purple, plain, plane, peculiar (as in Bear), and Penobscot.
Blessings and Bear hugs, friends.