Urban sport bike ussually stripped down to bare essentials, painted flat black, and held together by zip ties and duct tape. Think Mad Max. Often the result of a nice new shinny bike being laid down by a squid and sold cheaply by the rider or insurance company. Common in the SF Bay area.
Did you see that guy on the rat bike in West Oakland doing a burn out in a puddle of burning gasoline?
by Voneville August 16, 2005
A REALLY ugly motorcycle that is ridden often, never cleaned, and maintained at the absolute minimum for it to run. Some rat bikes are built from scrap parts (often from 4 or 5 different motorcycle brands), others start off as nice bikes and gradually become rats. They are often spray-painted camo or matte black to cover all the rust.
by yargh January 3, 2005