You short the USD by borrowing in USD, spending USD while it is still valuable and then wait for it to devalue. Deflation is a bad thing so the Fed won't let it happen.
Of course the flaw with this is that I get 4% interest on personal loans so I actually can't make money off of this strategy.
Of course the flaw with this is that I get 4% interest on personal loans so I actually can't make money off of this strategy.