The OED defines the adjective ‘indecorous’ as ‘contrary to, or wanting, decorum or propriety of behaviour; in bad taste’. This word came to mind when Y-H-B was eating breakfast at Up for Breakfast in Manchester Center, Vermont, as is his wont whenever he is in Vermont on a Sunday. Mind you, this word was unearthed from his memory in inner speech––all thought being in language––while recalling a meal in Manhattan some years ago, to which he had invited a couple from Los Angeles. They had asked whether they could bring a friend with them, and Y-H-B ended up paying for her as well as the couple because he thought at the time that it would be indecorous to ask the friend to pay for herself, once she had joined them for the meal.
Decorum is not limited to the behavior of others. In evaluating one’s own behavior, propriety as a criterion naturally obtains in all spheres, including the treatment of strangers.