Two prominent market voices squared off over cryptocurrencies in a debate that ended with a bet over a T-shirt. : Two prominent market voices squared off Wednesday over the future of cryptocurrencies in a debate that ended with a bet over a T-shirt. Economist Nouriel Roubini, who for many years wore the sobriquet "Dr. Doom," said bitcoin and its peers don't even deserve to be called "cryptocurrencies." Investor and former hedge fund manager Michael Novogratz said Roubini is underestimating the sector's future, and challenged him to put his pride where his mouth is.