Comedy, it’s often said, is hard. Just don’t tell that to Cameron Diaz, who can’t help but laugh when she talks about her new pic, Columbia’s “Bad Teacher.”

“I am the bad teacher,” she said, giggling. “She’s a horrible teacher. Some people really feel doing a good job is important. She takes pride in not giving a shit about doing her job and doesn’t care who suffers. She’s focused on herself, a narcissist. And she’s a lot of fun.”

The role of Elizabeth Halsey was not an immediate go when Diaz read the script.

“I was scared of her at first. The first 20 pages I was, ‘Oh my god there’s nothing redeeming about this character’ and I couldn’t stomach her. By page 30, I loved her and it became, ‘She’s amazing and I want to be her.’ By the end, I was cheering her on. She does what all of us wish we could do and say.”

Next up, Diaz circles Shirley MacLaine’s comedic aura in the London-set remake of the heist comedy “Gambit.”

“It’s very different from the original,” she said of the new screenplay by the Coen brothers. And in Michael Caine’s role, “Colin Firth is just the man,” says Diaz.

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