Very possible to short Bitcoin.
Just move your Bitcoins to
Okcoin. It is the cheapest option as other exchanges have large markups that you have to wait $1 price moves in order to profit. While in
Okcoin, you could already profit in 50 cents move.
If you're a gambler,
Okcoin has 20x margin trading. Bitfinex only 3x.
Okcoin is insolvent. Don't send a single satoshi to them. They've resorted to scamming and I would avoid dealing with anyone who mentions them.