I really do not think that anyone figures out 'the worst day of their life' in rational terms - the worst day of my life was not 9/11, or the day the US failed to ratify Kyoto, or the day Martin Luther King was assassinated, sorrowful as I was on all those occasions and bad as the effects on the world were. Nor was it the deaths of various friends, various occasions when doctors seriously screwed up my body or the day I failed to get a first-class honours degree.
It was probably the day that the woman I was in love with at the time rang me up at the behest of her other lover and said that she was severing all ties - even though there was a lot more of that story and I got to be very horrible to that other lover in due course. Or the day that a close friend came round and told me what a total shit I was - even though I knew at the time that this was bullshit, and years later we totally got past it.
The worst day of your life is the one you felt worst about at the time, and where the memory of that pain still hurts. AND THAT IS NOT ACCESSIBLE TO FRAKKING REASON OR THE PHILOSOPHIC CALCULUS OF JEREMY FRAKKING BENTHAM.
Sometimes, eg now, I despair of fandom.