Noble class believed to be breeding only between themselves and thus slowly degenerating.
They are the target of the famous "The Aristocrats" joke told by many stand-up comedians.
So the term can be used for people supposed to have pervert sex with their family members and family animals in the most disgusting ways one can imagine.
I hope there is no reincarnation. I wouldn't like to become the dog of those aristocrats living next door.