A person who deserves to be degraded not only in the sense of being a mother fucker, but must also be degraded as having a foul smelling asshole. A more direct explanation would be a person who is a pooh but mother fucker. Generally someone deserving of this degradation is considered to be of the backwards and foul smelling nature such as people who are fuckups in the slum of society. It can also be used to degrade any person to this lower level of humanity out of anger or distaste of that person.
I was going out to my car after banking mad chips at the casino and some poohbutmofo jacked my car.