As "Faux pas"? Grossly faux, of course. [But then, it is French, and not particularly colloquial] - I would be doing this translation either verbatim, or would use a substitution by explanatory phrase, like "tactlessly creating an embarrassing situation". The closest expression coming to mind would be "He should be the last person to speak of it...", but that might be more specific than the context requires.
"V dome poveshennogo o verevke ne govoryat" (proverb) =
[One doesn't mention the rope in the house of one who has been hanged] - the meaning approximates: this is neither the place nor the person to speak of these subjects, or "[he] should be the last person to be heard from on it"- with the same meaning that [his] input would be out of place and best if not provided.