If someone is sanctimonious, they behave as if they are morally better than other people, and it is annoying. We only use the word with a frown. A sanctimonious speech sounds holy and kind but makes you feel small. The old root is about being holy; though actually, today it is not only a church word. People use it when someone lectures you about food, money, the planet, or 'the right way to live,' while looking down on you. It is a bit formal and a bit sharp — more at home in essays, reviews, and arguments than in a child's mouth. Hypocritical is a neighbour: that word points at the gap between what you say and what you do. Sanctimonious points at the holy face the person puts on, even when they believe themselves. It is never a compliment.