Remember this.
Most people who try to get into fights usually have nothing to lose. Case in point your little counter boy, he is a minor with no assets, nothing of value and no repercussions because of his minor status. You on the other hand have things to lose.
Equally important is the fact that there comes times in a mans life that he has to engage in laying some smack down. Regret is a terrible thing, if your going to regret not doing something about this situation and losing self respect in the process then I say you have a decision to make.
All reasonable intelligent men use their minds first and their hands second. Outwit him or beat him down. But do it fast.
Good luck.