A person whose body is grossly out of proportion due to excess fat.
A very overweight person with the metabolism of a slug.
Being a fat ass can make you miserable because you begin to think you can't lose that weight.
Some people are proud of being a fat ass, but most people aren't.
Some people can't help being a fat ass due to medication or other medical conditions.
Art: Yea, he sure is a fat ass. Girls must laugh at that sucker.