The first time I saw the "rat" term used was in a bike mag, in the early '80's. It was a rusty old Harley with new tires and a blanket seat cover, with a screwdriver for an ignition key. Ratty!
I agree with the guys who say, "chuck all the silly names, a rod is a rod!" A Renault Dauphin with a Porshe engine is still a hot rod!