I've heard about as many different stories of the origin as they're are different types of "Hot Rods". But the one I've heard the most is the derivation from "Hot Roadsters". Also heard quite a few say it derived from stroked motors IE: "hot rods" as in connecting rods. Who really knows. "Hot Rodders" was a derogatory term used to describe the type that messed with the hopped up, cut down, cars. Kinda like "Holligans", "Punks" or "Greasers". I believe even "Rat Rod" was not a compliment when first used.......................