George Clooney and Brad Pitt
Jeff Vespa/Getty; Gilbert Flores/Celebrity Photo
is notorious for playing pranks
on his costars while filming. But he also has his sights set on his friends – specifically Brad Pitt
, who's the frequent butt of his jokes
"I have done some horrible things to people. Truly, truly horrible," Clooney, 50, admits on the season premiere of Bravo's Inside the Actors Studio
(Jan. 31, 7 p.m. ET). "I'm working on one right now for Brad Pitt. It might end his career."
"I owe him, so I'm getting him," he added.
If the prank comes to fruition, Pitt, 48, will find himself in good company. The long list of Clooney's other practical joke victims includes their Ocean's Twelve costar Julia Roberts
"I'm a big believer in making sets fun in general," Clooney tells Inside the Actors Studio
host James Lipton.
So what exactly does Clooney have up his sleeve for his pal?
"I've been working on it for two years," Clooney told the audience. "I'm not going to tell you what it is, but just know, I got it."