4. Kevin Costner - Robin Hood: Prince of Thieves (1991)
A really deplorable half-arsed effort here as Costner leaves it last minute to brush up on his British dialect, and decides to sporadically use it whenever he feels like trying in 1991's Robin Hood: Prince of Thieves. It's painful and quite saddening as Costner is a decent actor, but instead of stealing money from the rich, he should have nabbed himself a decent accent. He doesn't seem to even try, like a modern day Sean Connery, and his heart just isn't in it. He knows that it's beyond him and he's like a deer in headlights, perplexed and staggering through his lines with little conviction. When even Christian Slater is out-performing you you're in trouble. Costner really isn't great at any accent other than his own surfer-boy Californian, which makes for a hip and rad Robin Hood, but just one that sounds American in a time where America hadn't even been discovered, that's all.