Dear Joyce, What to do about name-calling?

Dear Joyce, My 4 year old son, Daniel, was upset at me the other day and called me The Stepmom.  I believe he was referring to Cinderella’s mean stepmom.  Then a few days later, he called me a witch, when I asked him to do something he didn’t like (I was asking him to buckle in his car seat).  I was so shocked I didn’t know what to say other…