be on (one's) high horse

be on (one's) high horse

To be adopting a haughty attitude of moral superiority. My sister was a troublemaker as a teenager, yet she's always on her high horse, lecturing me about everything. The radio host has been on his high horse all week about people sponging off the government, despite the fact that he is a known tax dodger.
See also: high, horse, on
Farlex Dictionary of Idioms.

be/get on your ˌhigh ˈhorse

be annoyed because you think that somebody has not treated you with enough respect: When they suggested that she might have made a mistake, she got on her high horse and asked them how they dared question her ability.
See also: get, high, horse, on
Farlex Partner Idioms Dictionary

on one's high horse, to be

To put on airs; to behave arrogantly. As long ago as the fourteenth century, persons of high rank rode very tall horses, a custom that came to symbolize superiority and arrogance. By 1800 or so, to be or to get on one’s high horse meant to act superior, with or without justification.
See also: high, on
The Dictionary of Clichés by Christine Ammer
See also:
  • be/get on your high horse
  • on one's high horse, to be
  • on your high horse
  • on (one's) high horse
  • on high horse
  • on one’s high horse
  • on one's high horse
  • get on (one's) high horse
  • get on your high horse
  • climb on (one's) high horse