I haven't attempted to watch these again in many years, but:
Gone With the Wind and Casablanca.
I felt they were just simply boring. I may eventually give them another shot, now that I am older.
One I'm a little ashamed to admit that I don't like is:
The Good, The Bad and The Ugly.
I love A Fistful of Dollars (and even the Bruce Willis remake, Last Man Standing) and For a Few Dollars More, but when it came to the third movie in the Man With No Name, I didn't care for it. I'd rather watch High Plains Drifter or The Outlaw Josie Wales.