From Longman Dictionary of Contemporary Englishbe/get on your high horsebe/get on your high horseBOASTto give your opinion about something in a way that shows you think you are definitely right and that other people are wrong If she’d get down off her high horse for a moment, she might realize there’s more than one point of view here. → high
Examples from the Corpus
be/get on your high horse• All right, all right; don't get on your high horse.• Oh, now he gets on his high horse and accuses me of being an anti-Semite!• Don't get on your high horse with me. 