What should parents never do in front of their children?

Abuse or violence. A long time ago, when I was a child, I remember a relative hitting his wife for dropping a tray of drinks at a gathering. Me and my cousins were playing in the kitchen and we saw it but that idiot of a man didn't care. I told my mom about it and she looked visibly upset that I witnessed the whole thing, and told my dad. But I don't know if dad confronted that man. So no, on top of everything else everyone has said, don't ever ever ever abuse (physical, emotional, mental) any person or animal in front of kids. Some kids remember it for life like me while others might just emulate it since it seems ok for adults to do it.