on one's high horse

on one's high horse  {adj. phr.},  {informal}

1. Acting as if you are better than others; being very proud and scornful.

Martha was chairman of the picnic committee, and at the picnic she was on her high horse, telling everyone what to do.

Mrs. Jones asked to see a less expensive hat. The salesgirl got up on her high horse and said the shop did not sell cheap merchandise.

2. Refusing to be friendly because you are angry; in a bad temper.

Joe was on his high horse because he felt Mary wasn't giving him enough attention.

Contrast: OFF ONE'S HIGH HORSE.