And especially screwed if you owe the broker more shares than are currently available to buy on the market @ $700. You have no direct way to cover your bet, and are naked. That’s when it gets really expensive, and you have to offer more than $700 to shake loose more shares, further driving up the price.
And if anyone thinks this is crazy and not connected to reality, out in the real badlands, other people are probably making huge derivative side-bets on this that don’t involve any actual stock.