George Clooney has ruled out ever dating Sandra Bullock because she once went out with one of his pals. The Hollywood superstars have been friends for 20 years and recently went through a tough time together as they filmed harrowing space disaster movie Gravity. But despite both of them being single, Clooney insists the fact Bullock once hooked up with one of his friends takes her out of the running as a potential girlfriend. He tells E! News, "She was dating one of my best friends. There's a certain bro code, you know what I mean? I've known her a long, long time."