I think there were a few key events but the one that really started it off for me was when my parents divorced. My Father got re-married (to another ex-jw) and they were promptly disfellowshipped.
What really did it for me though was no one (including family, siblings - still to this day) would speak to my Father. Yet in most of the divorce proceedings he was acting magnanimously towards my Mother, holding to a Christian attitude. Whilst my Mother, who was acting psycho, bitter and twisted (incl lying) - and acting in the most un-Christian manner - was still not only accepted by the Witnesses, but they took her side completely. Because of course my Father was 'wrong' by simple virtue of being disfellowshipped!