"Get off your high
horse" is an idiom people retort with in an argument when the other
person is acting like a holier-than-thou being when in reality, they aren't. To put it in a simpler manner, to tell people to stop acting as if they're the
top authority when they aren't.
Person A: "I am completely entitled to go around dismissing people when they do something completely
normal just because they're
wrong and I'm ultimately right."
Person B: "Get off your high
horse."