How do I talk to my child about a denigrating comment my ex said about me? Should I even go there?

My ex and I separated four years ago and we have a five-years-old kid; post separation our relationship has had its ups and down, but we've been mostly respectful and cordial with one another. That changed a few months ago after a disagreement that we couldn't resolve among ourselves and I had to take her to the court.Communication between us have become increasingly difficult, even though I only reach out to her to talk about matters related to my kid. Anyway, last week I was talking with my kid over the phone and a few minutes into the conversation I overhead her saying something along the lines of "you don't have to keep talking if you don't want to".I told my kid to hand over the phone to his mom as I wanted to ask her not to interfere with our conversation and he responded "mommy doesn't want to talk to you because you're an idiot". I was taken aback and I gently scolded him not to use that language and she did as well, but I'm pretty sure that he did not made this up.Should I leave it as that? I don't want to say something negative about his mom, but I just want to make sure that he understand that this is not proper behavior. via /r/Parenting http://ift.tt/2oGOxsd