Seems to be a mix betwen of "Je m'en bats les couilles" and "Le train de tes injures roule sur les rails de mon indifférence", never heard the author version. I stand wrong on the etymology, see below. French-speaking here.

It exists as an entry in the https://fr.m.wiktionary.org/wiki/s%E2%80%99en_badigeonner_le... but I don't think I ever heard someone uses it. The non vulgar original version seems to be "s'en brosser le nombril avec le pinceau de l'indifférence" (To brush one navel with the brush of indifference) and found it's origin in the comic strip Achille Talon.