A line people use when they get confronted directly for acting like a cunt to try to save face. It is normally used on people of equal or lower social standing and not generally used on people with power or authority. It is a pre-packaged response designed to win over the crowd or turn the tables and doesn't actually have any bearing on who is right or wrong.
Person 1: "Did you see Mark trying to hide his hair loss? It's so obvious."
Person 2: "Making fun of people's looks is kinda lame."
Person 1: "Get off your high horse."