Il y a des gens niais qui se connaissent, et qui emploient habilement leur niaiserie.
There are foolish people who know and who skillfully use their folly. François de La Rochefoucauld, Maximes (1665–1678), No. 208. Translation: J. W. Willis Bund and J. Hain Friswell (1871). Variant: There are foolish people who recognize their foolishness and use it skillfully.