holier-than-thou
holier-than-thou {adj.}
Acting as if you are better than others in goodness, character, or reverence for God; acting as if morally better than other people.
Most people find holier-than-thou actions in others hard to accept.
After Mr. Howard stopped smoking, he had a holier-than-thou manner toward his friends who still smoked.
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Source: A Dictionary of American Idioms
