It seems like everyone's trading Tesla at the moment. According to discount brokerage Degiro, the electric car maker was the most-traded stock among its Ireland-based clients in January. Indeed, Tesla was the most-traded stock in nine of the 18 countries in which Degiro operates. It's easy to see why – for a large-cap stock valued in the region of $150 billion, the price swings have been absolutely crazy recently. The stock, which more than doubled in the closing months of 2019 to end the year at $418, soared from $650 to $969 over a two-day period last week before tumbling back below $700 the following day.

High-profile short-selling outfit Citron Research, which went long on Tesla in 2018 and promised it would never bet against the stock again, last week announced it was going short once more. "We love $TSLA", the firm tweeted, before adding that "even Elon [Tesla chief executive Elon Musk] would short the stock here if he was a fund manager". That's debatable. Betting against bubbles is a dangerous business, as shorts have discovered in recent months. Six months ago, a quarter of the stock had been sold short. Many of those shorts have since been forced to close their losing bets and buy back the stock, resulting in what Ritholtz Wealth Management's Josh Brown calls the "greatest short squeeze of all time". Tesla is outrageously overvalued at these levels, of course. Traders buying the stock are playing with fire, but the only thing riskier than going long on a bubbly stock is going short.