The final fight against Sephiroth at the end of FF7.
I just got that far and realized that I simply did not care how the story ended. I'd had Aeris benched for most of the game so her death really didn't bother me, I never really cared about Cloud's story (seriously, it's like a Mary Sue written by a 14 year old), Sephiroth struck me as trying FAR too hard to look badass without ever actually DOING anything (as opposed to, say, Kefka in FF6, who blows up the world and declares himself god-king of whats left), and all of the other characters seemed entirely incidental to the plot.
I also quit just before Sin in FF10 (same basic problem: I realized that I didn't care about any of the characters).
I don't think I've ever even attempted either of them.