Confucius says; "To learn and to practice what is learned time and again is pleasure, is it not? To have friends come from afar is happiness, is it not? To be unperturbed when not appreciated by others is gentlemanly, is it not?"

Let it slide. His negative karma will burn him in the end -- he undoubtedly will do this to others if he has disrespected you, and for it he shall acquire enemies.

Enemies with vendettas that in turn serve your own goals of vengeance. Only time will tell, but it is inevitable if this is truly the character he possesses and has displayed.

Or you could do it yourself. But repercussions always come in one form or another -- guilt, for example, where emotion in regards to the bad dealer do not belong.

A waste of life he is, but don't let thoughts and actions towards him waste your own life.