The noun decorum is behaving, dressing and talking in a socially correct manner while exhibiting politeness, orderliness and calmness.

Synonyms are propriety, respectability, decency, or civility.

The word origins from Latin decorum meaning “that which is seemly”, from the noun use of the neuter form of decorus meaning “fit” or “proper” and from decor meaning “beauty, elegance, charm, grace, or ornament”. It was first used in 1568 meaning “that which is proper or fitting in a literary or artistic composition” and in the 1580s “propriety of speech, behaviour, or dress, formal politeness”.

I can’t believe she has no sense of decorum.

Having a high sense of decorum is required when entering the palace.

Ken was reported for subverting school decorum by bullying his teachers and not following the school’s rules.