You may disagree with their politics, television choices or the way they parent their children, but it's not your place to interject your own preferences and particular parenting style. You are a guest, not a voting member of the immediate family. Even if you are the grandmother!
To have good manners is to consider the emotional well-being of someone besides yourself, which is why I have often emphasized the importance of saying "thank you" to anyone who has done something for you. But is it possible to thank someone too much?
Sometimes a well-meaning observation can just be annoying no matter the person's relation to you. Though we can't quite pull "My house, my rules" rank (you're still our parents after all), here is a list of six things you should never say to your adult children when you're visiting them.
When you're staying with someone, you're more considerate about making noise, cleaning up after yourself, listening to what they say, paying attention to their needs and rising to the occasion even if you're feeling crabby, because you have to.