Noun: A person, either male or female, who wastes a car salesperson's time when that salesperson could be doing something either more constructive or entertaining. Used as the strongest epithet for a non-buyer in the retail automotive industry.
"Would you believe that fucking Jack-off had Johnny test drive him in three cars then left without so much as a writeup!!" Also, "Beat it, you Jack-off!" Frequently shortened to "Jack", such as "What a Jack!"