(Decorous - characterized by dignified propriety in conduct, manners, appearance, or character)Example: "Members of the diplomatic corps are expected to behave in a decorous manner."
Use the word decorous just as you would use the word 'proper'.
Example: Bob has very decorous (a.k.a. proper) behavior when dining with the beaver weasels in Canada.
When it has a subject, verb, punctuation, capitalization, a predicate, and a complete thought. A sentence is a sentence when it is handed down by a judge (or a magistrate).