"Dirty words" were said by the people who worked in the dirt.
Inspired by THE POWER OF DIRTY WORDS | Norman Spinrad At Large: "In French-conquered England, the three classes spoke three different languages. The language of the conquering power was French, the language of religious power and high-toned intellectual discourse was Latin, and the language of the conquered natives who became the lowest class serfs had already been a proto-English “Anglo-Saxon.”"