Someone who's douchyness is too large to fit into a bag.
Can be used in place of douchebag where appropriate.
Can't believe that guy cut in front of me in line and spilt his drink on me while doing it, he's such a douchehorse
A douchehorse is someone who attempts to conquer Japan by sending a fleet of shitty riverboats to sea, then gets all surprised when every single boat sinks in a storm, resulting in the highest number of at-sea casualties in history.
That Kublai Khan douchehorse was a real douchehorse.