I've only walked out of a theatre twice, both in 1977. I don't know, but I'd guess that it was just because I saw so many movies that summer - I think I averaged three films a week all that summer. The ones I walked out of were
The White Buffalo and
Sorcerer.
Later on, I would have walked out of
The Mask, but I was with a friend and he really wanted to see it, for no good reason that I've ever been able to figure out.