If you are working should you remain professional?

So I have been to this buffet style restaurant two times and each time experience has been less than steller. Yes, food is good, but service is despicable. First instance a woman in the booth behind us found a piece of plastic in the filling of a puff pastry and had to take it out of her 2 year old daughters mouth. Instead of apologizing the server starts threatening to call CPS on the mother for letting the child eat that food. After that he tells them they can have the meal half price, They refuse to pay after that and the couple with the daughter say, "we are getting the f*ck out of here," the server goes on a tangent screaming "f*ck you, you f*cking f*ck f*ck f*ck f*ck" I wish I were kidding, but it was right in front of us. This behavior was appalling and not at all professional. My SO said he was completely in the right for responding like that, because they weren't going to pay, and made a scene. I think it was completely uncalled for. What do you guys think?