I had no final straw. What I professed to be rock bottoms at the time only got worse. If life was a movie I guess there would be a dramatic incident or some clear revelation but there was none. I don't really feel I gave up alcohol, more that alcohol gave up on me. Even the knowledge it was sure to kill me had no effect. I guess I got to the point where I was actually bored with myself. I guess I'm saying it was a gradually worsening process with many horrible and ever worsening incidents than a specific singularly dramatic incident. A also think luck, circumstance and synchronicity played their role.
That's just my own experience. I know many people who would tell you different. As a previous poster has said it is that feeling of being sick and tired with being sick and tired.