Now this is pranking at its finest! 

Matt Damon stopped by the "Tonight Show" with Jay Leno to talk about his upcoming flick with George Clooney "The Monuments Men" and shared one hilarious story about his costar. 

While the two have a great friendship, Matt was not immune to George's infamous practical jokes on set. Check out the video above to find out how Clooney secretly made Matt believe he was gaining weight!  

Poor guy -- but we gotta say, that has to be one of the most geniously calculated pranks ever. 

George is known for messing with his costars while filming, and since he was the director, producer and actor in "The Monuments Men," the 52-year-old had far more resources to pull off one epic prank on his dear friend Damon.  

 What do you think of Clooney's practical joke? Tell toofab in the comment section below!

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