By 'ah-Ha moment' I mean here, the point at which I came to the realization that there really is no such thing as god. Up until that point I considered myself agnostic. Maybe everyone has a moment like this. If so, I'd like to hear yours.
My 'ah HA' moment came when I read, watched news broadcasts and heard on public radio descriptions of all the devastation resulting from the 2004 Indian Ocean / Boxing Day Tsunami. I believe that over 230,000 people in more than ten countries were killed by this massive surge of water, including many tens of thousands of children. That last point confirmed for me that no such thing as god could exist if it would allow so many people to die needlessly. This was no manmade event like a war or floods and draught from global warming. This was a completely natural event which could have been stopped by the 'hand of God' or by some other divine intervention, if any supernatural being ever existed.