Farb was the worst insult in the hardcore vocabulary. It referred to reenactors who approached the past with a lack of verisimilitude. The word's etymology was obscure; Young guessed that farb was short for "far-be-it-from-authentic," or possibly a respelling of barf...

Farb was also a fungible word; it could become an adjective (farby), a verb (as in, "don't farb out on me"), an adverb (farbily) and a heretical school of thought (Farbism or Farbiness).
-Tony Horwitz, Confederates In The Attic