Manos: Hands of Fate! Truly Horrible movie! Yet, I've only seen the MST3K version, like you, which at least, makes it watchable! That's cool you are a MST3K fan, too!
As for movies that I have walked out on. None, so far. I rarely go to movies in the theaters (maybe 2-3 per year) and when I do I carefully pick them and read reviews about them. Last one I saw: 500 Days of Summer- loved it! Also, I'm probably the only person on here that finds Talladega Nights to be hilarious. I guess you need to have some sort of twisted humor to like that movie!