adjective
indecorous
in-DEK-er-us/ɪnˈdekərəs/
Not meeting accepted standards of proper behavior.
The guest's loud laughter and sprawling posture are indecorous during the solemn ceremony.

Etymology
Latin decorus described what was fitting or becoming; its negative marked what was unbecoming or unseemly. Applied to conduct, this judges whether behavior suits the situation and meets expectations of propriety or good taste.
In context
what is indecorous about this painting well how about the first monumental representation of the Virgin Mary's cleavage in the history of art
More examples
- Shouting across the courtroom is indecorous.
- She apologizes for her indecorous remarks about his salary.
- The board chair refuses to tolerate indecorous behavior at meetings.
Forms
indecorous
indecorously adverb — In a way that violates social standards.
Similar words
- improper
- Broader term covering violations of rules as well as social standards.
- unseemly
- Emphasizes behavior that looks inappropriate for someone's role or situation.