Green’s Dictionary of Slang

a country bumpkin, simpleton.

1920

Ade Hand-made Fables 81: This Traveller was a City Yap, which is worse than being a Begosher, because the R.F.D. Boob usually knows that he is below Par.

(US drugs) a drug addict who travels between small towns, hoping to persuade sympathetic or naïve doctors to write narcotics prescriptions.

1938		D. Maurer ‘Lang. of the Und. Narcotic Addict’ Pt 2 in Lang. Und. (1981) 108/1: r.f.d. dope-head. An itinerant addict who depends for his narcotics upon small-town or country doctors.
1942		Berrey & Van den Bark Amer. Thes. Sl.
1949		Monteleone Criminal Sl. (rev. edn) 193: r.f.d dopehead A drug addict who travels about the country or small towns to obtain his supply from doctors.
1959		J.E. Schmidt Narcotics Lingo and Lore 158: R.F.D. – A peripatetic drug serf who moves from one small community to another so that he might shark narcotics or prescriptions therefor from the unsuspecting practitioners of the hippocratic profession.
1967		Maurer & Vogel Narcotics and Narcotic Addiction (3rd edn) 383/1: RFD junker, RFD gowster, dopey, dope head, floater, cross-country hype. An itinerant addict who depends for his drugs upon small town or country doctors.

(US) a homosexual living in a rural area, outside the main gay world.

1941		G. Legman ‘Lang. of Homosexuality’ Appendix VII in Henry Sex Variants.
1965		Guild Dict. Homosexual Terms 39: r.f.d. queen (n.): A homosexual who lives in the country or a very small town and does not understand the argot and ways or habits of the fraternity in metropolitan areas. From Rural Free Delivery, it suggests the country scene.
1972		B. Rodgers Queens’ Vernacular.