A couple of the most boring (and overall worst) movies ever made were ones I got up and walked out on:
“The Last Married Couple in America” — way back around 1980, supposed to be a comedy but just a God-awful dull sack of excrement!
“American Splendor” — around 2003, was supposed to become some cult classic about the “art” of underground comic books, starring Paul Giamatti, but this POS is so boring, stupid, and all-around horrible that there should be ritual executions of everyone involved in its creation.
Maybe you had to be both a fan of his comix and a current/former resident of Cleveland as I am to appreciate that movie.