Actually, I think it was smart for Kevin Costner to avoid the accent instead of mangling it.

I nominate Brad Pitt in anything except Snatch.

Rob Morrow's Boston, um, "accent" in QUIZ SHOW.

To this day, the worst I've ever heard that instantly springs to mind. I still blame him for the demise of "Northern Exposure".

My boss just yelled across the room...Dick Van Dyke in Mary Poppins.

Give Keanu Reeves a gander in Francis Ford Coppola's Dracula. His, um, "british" accent sounds like a third grader doing a Benny Hill impression.