Bitcoin is a call on a generalized currency collapse. From Nick Giambruno at internationalman.com:

As told in the movie The Big Short, a group of hedge fund managers who saw the housing crash coming used Credit Default Swaps (CDS) to make a fortune.
These exotic financial instruments conveyed information crucial to seeing the 2008 financial crisis in advance. That knowledge allowed astute speculators to get positioned for massive profits as the crisis unfolded.
In the coming crisis—which has already started—I expect CDS will again play a key role in telegraphing important information shrewd speculators can use to their advantage.
A CDS is a contract between two parties. Think of it like an insurance policy against a borrower—typically a large company or a government—defaulting. One party underwrites the insurance policy, and another buys it. If the borrower defaults, the CDS issuer pays out the CDS buyer.
CDS trade in the open market and reflect investor expectations of the default probability of a particular borrower. The more likely the underlying entity is to default, the more expensive the insurance (CDS) will cost.