Funny story.
Anyways, if he really was asked to remove the tie, and he refused, he really wouldn't have any case in a wrongful termination suit...well, unless he has a weasely lawyer who decides to claim that he wasn't fired for the tie, and claims it was because he was black or something.
I do think the car dealership was perfectly justified in firing him though. That absolutely can affect his ability to make sales, and if he refused to take the tie off, then its an issue.