for me, it's Prince of Darkness which i saw back in the 1980s. my friends and i were waiting for the face of the prince to be shown but it was never done. all was shown was his hand coming out of a mirror in the last part of the film. it's really trash - waste of money and time.
I don't remember nay boring movies that I watched. I didn't watch movie much that's why if I will watch one, I am sure it will be exciting. I guess, the most boring movie is if most of the scene the character are keep on talking with no thrill and excitement at all.