Karl Popper, Bears, and Fossil Rabbits in the Precambrian

Fossil rabbits in the Precambrian.
       — J.B.S. Haldane (when asked what would disprove evolution — may be apocryphal)

I’m getting a little tired of confirmation bias and lack of falsifiability among bears. It doesn’t matter what data point comes out — inventories, housing, rail traffic, GDP, jobs, etc. — bears continue to find ways to deny twelve months of market advances, while spinning compelling stories of imminent collapse. Yes, I’m deep in the cyclical bull, secular bear camp with my friend Barry — which is like Jeremy Grantham’s "seven lean years" — so I’m far from sanguine over the long term. But at least I’ve been willing to countenance that the current rally has been built on something at least semi-sustainable.

So, for the hard-line bears out there, what are some specific, measurable and realistic things that would falsify your view that this is all illusory? Lay ’em out in the comments.