The term rice rocket was for motorcycles not cars, originally. The term came out before cars were modified in the way they are now. Rice rockets usually described Japanese bikes that were superior performers off the line, were more likely one up bikes, and cafe style, before european cafe was cool. Further, Most Harley bikers knew they would be smoked in a drag race so to save face, knowing they were more in love with tradition than technology, had to rationalize their decision making process in purchasing a knowingly inferior product by, coining the term "rice rocket.
Those guys on their "rice rockets" don't know what real biking is all about!