1. Ted really acts like he thinks he’s the boss around here. He’d better get off his high horse pretty soon or he’ll have no friends.
2. Who do you think you are coming in here and ordering me around like this? Get off your high horse!

The expression originates from the custom of high-ranking officials traveling on horseback, while commoners walked. The physical height of being up on the horse is equated with being in a superior position.