As far as methods for shorting bitcoin, I just had read that EToro plans to support BTC in one or more currency pairs. So there are more methods coming.
https://bitcointalk.org/index.php?topic=153742.0The above is also a method of profiting from the collapse of USD/BTC. You can select from a wealth of maturities, options types and trading strategies, the one that you think will maximize your profit with the minimum risk. You will never risk more than you have deposited. All contracts are guaranteed by the house to have functional buyback terms if you want to close it before maturity.