What do you mean a joke? Looking at the blockchain, it seems to be a full fledged, serious, Ponzi scheme. They're taking in BTC and paying it out again to the early investors.
Even though it is a functioning ponzi scheme, it could still be classified as a joke. I'd go so far as to say if you don't see humor in it there might be something wrong with you.
Although there is the legal question. I'm not sure it would be so funny to tell it to a judge.
EDIT: +1 to ryanjshaw for showing the blockchain: https://blockchain.info/address/1ponziUjuCVdB167ZmTWH48AURW1...