You can say get off your high horse or get down off your high horse to someone who is talking as if they are better than someone else. You can also say come off your high horse.
Stop criticising everyone! You should get down off your high horse and admit that you aren't perfect either!
John used to tell his fellow classmates what a genius he was. But after he got a couple of bad marks, he had to come off his high horse and study as hard as everyone else.
To back the wrong horse means to support someone who can't win.
Our boss should have promoted me to senior management. Peter doesn't have enough experience to be in that position. The boss backed the wrong horse!
Archaeologists think that horses were first tamed and exploited by humans some 6,000 years ago in west Kazakhstan.