Technically The Aristocrats is not a filthy joke
Personally I think it's disingenuous to call this joke the most disgusting/filthiest joke of all time, because the disgust and filth all come from the improvised ad libs to the joke. In fact, it's perfectly possible to tell a totally clean version of the joke and still have it work - you just need acts that are the opposite of what would be considered aristocratic, so the punchline still works if you had the family running around doing farmyard animal impressions.
If you call this the most disgusting/filthiest joke then you have to also explain why any joke with an improvised section couldn't be made equally disgusting.