You know how irritating in-laws can be? I think I am discovering the reason why that is now that I are one. It is a lot like when you have your first child. As a new parent you feel that your life and ability to parent is on trial and when your child screws up it reflects badly on you. Well guess what? That feeling intensifies when that child grows up and marries. Then you get to watch them run their own household and you find yourself thinking things like:

"I thought I taught her how to clean better than that!"
"Why in the world are they eating THAT?"
"Why did they buy ______ when they clearly can't afford it?"
"Why doesn't she/he raise my grandchild better than that?"

The temptation to give advice so that the child won't be a failure as a housewife, husband, or parent and therefore a bad reflection on you is very strong. I have developed a callous on my tongue from biting it so many times. But I made a vow to myself when my children married: I would not give any advice unless asked for it. I also vowed that I would not cause my children to feel like they were about to undergo a white glove inspection when they saw me coming for a visit.