Michael Rapaport on Justified. I hated the guy before then, but I wanted him to DIAF the first time I heard him attempt a southern accent. Just an awful casting decision.
But I forgot about the guy who played "Harris" in Major League. Dude looked like he was 55 years old in that movie. Corbin Bernsen barely could pass for a ball player, but ol' Harris wasn't remotely believeable. Still a great movie though.