Diaz gave her perspective on relationships as she and Leslie Mann promoted their new comedy, The Other Woman, at CinemaCon, the annual convention of movie exhibitors, in Las Vegas.
The two ladies joked around with each other as they talked about the film, in which Diaz's character discovers her boyfriend is actually married to Mann's character and the pair team up to seek revenge.
In real life, Diaz insists that everyone has been the victim of a cheating partner.
"At some point in your life, everybody has been cheated on," she said, laughing. "I'm not saying that the relationship you're in currently, you're going to get cheated on, but eventually or maybe in the past it's happened."
And if you think you are the exception to the rule, Diaz has news for you: "You've never been cheated on? You've never been cheated on ever? Really? Really, nothing? Oh good. Well, guess what? You may not know that you've been cheated on."
The 41-year-old actress also weighed in on the "conscious uncoupling" of her friends Gwyneth Paltrow and Chris Martin.
Paltrow and Martin, who were married in 2003 and have two children, announced their split on Tuesday in a message on the actress's blog called "Conscious Uncoupling".
Diaz said they were handling divorce the right way "because everybody is interested and they are giving them the truth".
She added: "They're being very honest about their relationship, which is that they are really great friends, they're amazing parents and they're just consciously deciding that a part of their life is not going to be spent the way it's been for the last 11 years, which I think is ..."
"Eleven years is a long time. That's a long time. It makes sense," added Mann.
The Other Woman opens in US cinemas on April 25