[aredox]

>I can’t decode French elitism.

It is a clear case of "langue-dans-la-joue"

(or is it "langue-dans-la-fesse"?).

[samzub]

It would not be "langue-dans-la-fesse" for sure, even if this expression is very humoristic itself! Tongue in cheek can be said "pince-sans-rire" : https://fr.wikipedia.org/wiki/Pince-sans-rire

[Xmd5a]

pince-fesses obviously