The pair, which also starred in hit TV show Boardwalk Empire, play ruthless criminals in the film and they decided to test out their acting skills by freaking out fellow travellers.
Pitt admits the actors found the stunt hilarious, but the other passengers were far from happy.
He tells New York Post gossip column Page Six, ""We met in an airport, We started running our lines in front of people, like on the airplane, to see if we could get away with it. (Our characters) are gangsters so they're talking about shooting people in the eyeballs and stabbing them with ice picks... They (the passengers) didn't know we were kidding, you know, which was funny.""