In context: It is no secret that Apple CEO Tim Cook and Facebook CEO Mark Zuckerberg are not friends. They have traded backhanded insults and indirect jabs for years. Part of the conflict comes from the differing philosophies. Namely: how to make money off a free product versus a sold product.

While Tim Cook's barbs are never pointed directly at Mark Zuckerberg, they always seem to trigger the Facebook founder into a sometimes irrational response.

In an interview back in April, Cook told MSNBC, “We’re not going to traffic in your personal life. Privacy to us is a human right. It’s a civil liberty.”

The remark was in reference to the possible regulation of companies that use and sell the personal data and browsing habits of their users. The wake of the Cambridge Analytica scandal was still fresh, and the comment reportedly angered Zuckerberg.

On Wednesday, The New York Times published a scathing exposé covering Facebook's involvement in everything from the Russia investigation to sex trafficking legislation. The article noted that according to a source, “Mr. Cook’s criticisms [on MSNBC] infuriated Mr. Zuckerberg, who later ordered his management team to use only Android phones — arguing that the operating system had far more users than Apple’s.”

“When an online service is free, you're not the customer. You're the product.”

Thursday morning Facebook confirmed Zuck’s feelings on the matter and tried to clarify his response. The lengthy blog post seemed to be an attempt at a PR reversal calling the NYT piece "inaccurate," but one point addressed Cook’s criticism directly.

“Tim Cook has consistently criticized our business model, and Mark has been equally clear he disagrees. So there's been no need to employ anyone else to do this for us. And we've long encouraged our employees and executives to use Android because it is the most popular operating system in the world.”

This latest instance is not the only time Cook has made comments that got under Zuckerberg’s skin.

In 2014, Tim Cook told Charlie Rose in an interview, “When an online service is free, you're not the customer. You're the product.”

He repeated that refrain in September in a statement on Apple’s privacy policy. Taken in context, Cook probably had Google in mind, but Zuck did not allow that to stop him from getting annoyed about it.

“A frustration I have is that a lot of people increasingly seem to equate an advertising business model with somehow being out of alignment with your customers,” Zuck told Time. “I think it's the most ridiculous concept. What, you think because you're paying Apple that you're somehow in alignment with them? If you were in alignment with them, then they'd make their products a lot cheaper!”