If I were an etiquette authority, these are the two sentences I would proclaim banned from polite conversation:
(1) "You look tired." Because really, if you don't feel tired, you don't want to hear this. And if you do feel tired, you don't need the reminder. Or the news that you are broadcasting your inner climate to the world.
(2) "You look like your mother/father." Because there's at least a 50% chance that the child really, really doesn't want to grow up to resemble his/her parent. At least.