it'd have to be robbing a bank. get enough money from that and you can have pretty much all you want so no need to commit more
Rob a national bank of every single last yen they have (the currency with the worst exchange rate, worth less than a penny). From their gold slabs to the last yen. I would have said murder, but I would prefer to do that and not get caught when police are trying to find me, gives me a better gratification.
I would hack into some major corporations largest bank accounts and transfer all the funds to one remote account under a false name.