When my ex acts in an indefensible manner, I simply remind my kids they can work on their skills for dealing with a difficult person without criticizing their dad. Although it may be tempting to offer your critique of what the other parent is or is not doing, even if the other parent does it when with the kids, you shouldn't.
Like most parenting moves, the high of being the cool, with-it, socially-connected dad lasted about all of no seconds. Or the time it took my daughter to say, "Oh God, why did you join Tumblr? Didn't you know it's just for 12-year-old girls to complain about their thigh gap?" In my head, I heard all the records everywhere scratch at once.