For me:
"Fletch." I grew up loving classic 80s comedies with Chevy Chase, like "Caddyshack" and "Vacation." Most guys my age love it, but I thought it was pretty average.
"The Departed." I think almost all of Scorcese's stuff is good to masterful, but this was just a mangled mess. There were some good lines and performances, but overall, a far cry from Scorcese's classic films. I can't believe this is the movie that finally got him an Oscar.
"E.T." I know it's universally loved and I thought it was great as a kid, but the luster wore off once I got older. I couldn't even sit through it now. Not that it's a bad movie, but it just doesn't hold adult interest as well as other kid-oriented films.