Sometimes people think it's funny to say things as cruel as "your head looks like it was run over when you were a child" and these people are SO incredibly daft that if you don't throw a fit right then and there, breaking down into hysterics, they think you must like it!

Tell this person to stop. Don't give him another chance. Report it to your superiors immediately and tell them it's been ongoing for quite awhile now. I think this may get the guy to finally stop. And if it doesn't, you definitely have a workplace harassment case.