There's also the small matter of liquidity. If you sell enough BTC to crash the price, you're still likely to get killed buying them all back to cover the short

There's also the small matter of liquidity. If you sell enough BTC to crash the price, you're still likely to get killed buying them all back to cover the short because: a) There's a lot more bids than asks. It's a lot easier to ratchet the price up than it is to lower it. If Mr Shark sold 50k BTC in one hit right now, he would move the price from $46 to $31. If he tried to buy 50k BTC in one hit, BTC would shoot up to $100 USD. b) Since the last crash and subsequent boom, there are lots of people now who yearn for the days of $5, $10 or even $15 BTC and will happily buy at those prices[1]. Mr Shark will be competing with their orders during his buyback. Strangely I think the first crash made bitcoin stronger. c) I'm not sure Mr Shark appreciates the psychology of the current bitcoin market. I think he assumes there are people sitting on a ton of BTC who are going to panic and sell at $5. Even a cursory reading of the bitcoin forums would show that this is not the case. [1] I sadly confess that the kool aid is delicious and I am one of them.