Billionaire Tesla CEO Elon Musk called investor Jim Chanos "Thanos" after he said he has shorted stock of the EV-maker. "We just think [Tesla's stock] is ridiculously overvalued," Chanos said. "Jim Thanos needs to stop snapping his gloves on his own investments," Musk said. A short position is when an investor bets against the market, profiting when share prices decline.