Words like passé, or even ostentatiously using the accent on the "e" when writing passé, are all cultural signals describing who we are, what we read and write,

Words like passé, or even ostentatiously using the accent on the "e" when writing passé, are all cultural signals describing who we are, what we read and write, how old we are, and what we find amusing. Culturally archaic expressions are all part of that, and they have their place whether being used "ironically" or not. I disagree that this person sounds like a fool for using the expression. They may sound older, much as I must sound when I use words like "hip" and "funky." In any event, "sounding like a fool" should be reserved for saying things that are foolish on the facts or content of the statement. I think there's plenty of room for civilized disagreement with that person's statement without worrying about whether they're signalling that they're part of your cultural tribe or not.