What investment(s) can I make to benefit directly from a crash in the Chinese stock market?

I want to short sell certain chinese stocks that have extreme high valuations, hedged with an out of the money call option, to protect my losses if the boom continues. However I read somewhere that chinese stocks cannot be shorted. Furthermore I tried shorting a chinese stock on etrade but it would not allow me to, Short sales in this security are not allowed, giving their reason as "We were unable to borrow the shares" Is it even possible to short chinese stocks??

You should short Chinese stock market indexes. The best way to do this would be shorting some of the Chinese ETFs such as FXI for example. If you want to a broader index (70 shares) you could short the iShares MSCI China Tracker (Bloomberg ticker: 2801:HK).

However, be careful as the Chinese stock market "bubble" might not be about to burst...

You can short-sell Chinese stocks.

Traditionally, you could short sell the Yuan, but we can't buy it. I would initiate a strategy of short selling and holding long positions. Start by finding the sector(s) you believe will suffer the most from the crash, and short sell them. Use the credit obtained from the short sell to purchase stocks in a sector(s) that will explode as a result of China's downfall. That way, you aren't really using your money. As the short shares drop in value, you gain a profit. As China falls, the long positions gain in value as investors flee from China to wherever your long position is held. When the profit comes to the bank, close your long positions and use that to cover you short positions. Take the gains and move on to the next objective.

sell walmart short.

That wouldn't be a wise move at this time, considering they are going through a growth boom now. Even Warren Buffet is investing big there.