As far as I can tell, there's no reason for his nickname of "Thoroughfare". His isn't employed as a toll taker, he doesn't play golf, and his first name doesn't begin with a "T" and his last name is simply Smith. When one of the girls in accounts receivable starts calling him "Tupperware" and the UPS guy says, "Yo, Thoroughbred!", because that makes just as much sense as "Thoroughfare", he's not only unamused but pissed. He also doesn't take too kindly to "Frigidaire", "Thurgood Marshall", or "Turgid Bear", which makes Penny the receptionist blush after she asks what "turgid" means.