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Top 10 Feuds of 2010

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Zach Galifianakis, Mel Gibson, Robert Downey Jr.

Krista Kennell/Sipa Press; Kevin Winter/Getty Images; Jeffrey Mayer/WireImage.com

7. Zack Galifianakis vs. Robert Downey Jr.

Costars don't have to get along. RDJ and Z.G. may have been together for Due Date, but when it came to Mel Gibson making a cameo in The Hangover 2, the duo divided. Downey believed in second chances (Mel game him one) and Galifianakis believed in not having crazy, racist men on set. For some reason, Zach's reasoning prevailed.