NEVER... the best thing that you can do for your children is to be CIVIL with the other parent NO MATTER WHAT. Don't inflict emotional abuse onto your child because you have a grudge against the other parent.
StepMomsAreUs: Co-Parenting with a Toxic Ex - Book Review. My summary of how great this book is for people who are going through a divorce or are in a blended family, it's a must read! (Step Father Wedding)