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This is a guest post by Zack Mandell, who is a movie enthusiast and owner of www.movieroomreviews.com and writer of movie reviews about movies such as The Departed. He writes extensively about the movie industry for sites such as Gossip Center, Yahoo, NowPublic, and Helium.

Back in February of this year, Meryl Streep won her third Academy Award for her stunning and incisive portrayal of controversial former British Prime Minister Margaret Thatcher in “The Iron Lady.” The reviews for the film, which came out in December 2011, were decidedly mixed, and criticized the film for its pretentious approach and inaccuracies.

The reviews for Streep, however, were once again unanimous raves. Mick LaSalle of the San Francisco Chronicle said, “Streep’s performance is so true and so uncannily accurate, so full and so complete in its understanding that she is fascinating every second she is onscreen.” Most critics also pointed out her uncanny mimicry of Thatcher’s storied accent, but of course, Streep is used to critical praise for her mastery of accents.

Indeed, all three Oscars she has won have been for performances in which she used different accents. She nailed Thatcher’s accent for “The Iron Lady,” her Polish accent was impeccable in “Sophie’s Choice,” and she had an American accent in “Kramer vs. Kramer” (admittedly, that one probably wasn’t too difficult for her). Yet while Streep is notoriously astounding at accents, she has many colleagues in the acting field that, well, are not.

Here are ten of the worst accents ever committed to the celluloid.

Dick Van Dyke in “Mary Poppins”

Many American actors will be asked to use a British accent at one point in their career, and many of them will inevitably fail. Yet for his performance in “Mary Poppins,” Dick Van Dyke is largely considered the most egregious offender. It’s hard to tell whether he modeled his ostensible cockney accent off of Michael Caine or Darrell Hammond’s Sean Connery impersonation for Saturday Night Live.

Jack Nicholson in “The Departed”

Unlike Streep, who has been consistently turning in phenomenal performances even late into her career, Jack Nicholson has pretty much coasted on being Jack, “About Schmidt” aside. In “The Departed,” a crime classic in every other respect, Jack doesn’t really even appear to try to deliver a credible Boston Irish accent. It doesn’t help that he’s surrounded by a cast of Boston natives the likes of Matt Damon and Mark Wahlberg.

John Wayne in “Conqueror”

A lot of people overlook this travesty on Wayne’s filmography, but the Duke was once cast as Genghis Khan for this Howard Hughes production. No, you read that right. Of course, Wayne doesn’t really bother with the accent. Apparently, he thought a pencil thin mustache was enough to be vaguely Asian.

Julia Roberts in “Mary Reilly”

Roberts had been criticized for her attempt at an Irish accent in a previous film, “Michael Collins.” As a result, she hired a voice coach to fine tune it for this 1996 Dr. Jekyll and Mr. Hyde tale. Given that her accent got even worse the second time around, her voice coach must have been the equivalent of Stevie Wonder as a football coach.

Keanu Reeves in “Bram Stoker’s Dracula”

Probably one of the most famous examples of a terrible attempt by an American actor at a British accent. But honestly, why did anyone expect him to nail the British accent when even his attempts at American accents are kind of iffy?

Kevin Costner in “Robin Hood: Prince of Thieves”

Costner was fresh off his two Oscar wins from “Dances With Wolves” when he starred in this 1991 Robin Hood film. Of course, those two Oscars were for film-making, not acting. Costner tries his hand at a paltry British accent for the first third of this movie, and then it just kind of disappears, along with his Academy goodwill for the rest of his career.

Mickey Rooney in “Breakfast at Tiffany’s”

On December 7, 1941, the Japanese military executed a devastating military air strike on Pearl Harbor that left over 2,400 Americans dead. As horrible as that day that lived in infamy was, it was no excuse for the Hollywood retribution: Casting Mickey Rooney as an Asian landlord in “Breakfast at Tiffany’s.” Rooney’s performance is over-the –top, strongly emphasizes negative stereotypes and is both shrill and offensive. It almost ruins what is otherwise a perfect film.

Nicolas Cage in “Captain Corelli’s Mandolin”

Nicolas Cage is an anomaly as an actor. When he’s good, his performances rank as some of the best in the medium. But when he’s bad, he’s rattling off an Italian accent so bad it sounds like a high school drama student auditioning to be a member of the Corleone family. What makes it worse is that Cage is himself Italian-American.

Nicole Kidman in “Cold Mountain”

This is one of those weird entries, in that the performance that Kidman delivers in this 2003 Civil War epic is actually pretty stellar in every other aspect. Yet her attempt at a southern accent only comes out on occasional line readings throughout the film. It doesn’t help that it’s just simply hard to buy one of the most glamorous film actresses of all time as a Civil War farmer, particularly when the filmmakers make no attempt to dirty her up and make sure she’s looking her Grace Kelly best at all times.

Sean Connery in “The Untouchables”

A perfect companion to Kidman’s entry on this list: Another otherwise solid performance marred by an atrocious attempt at an accent. In fact, Connery won an Oscar for his turn as an Irish cop on the beat in the Al Capone owned streets of Chicago. Yet Connery can’t shake the famous Scottish brogue film audiences have come to love over the decades. He couldn’t do it as a Russian submarine commander in “The Hunt for Red October” either.