The worst thing has happened, to someone, somewhere, at some point.
Given the axiom of choice, there is an event which all can agree is the worst thing to have happened.
There is an event which *all* could agree is the worst thing that has ever yet happened.
Given that there is an event in the past which is the worst thing that has ever happened so far, what's the probability of a future event that is even worse?
Is that the worst thing that *could* happen? Or is it just the worst thing that has thus far happened?
How much worse is the worst *possible* thing to happen?