The world's most popular social media platform has been on the back foot for months, including over the allegation that data from millions of Facebook users was abused by the consultancy Cambridge Analytica to help drive Donald Trump to the White House. Specifically, Cook said Apple was "not going to traffic in your personal life", and that to Apple privacy is a "human right" and a "civil liberty".
Zuckerberg called Cook's criticism "extremely glib", and apparently he was seething behind closed doors.
The zing earlier this year that might have upset Zuckerberg came during an interview on MSNBC.
Infuriated by Mr Cook's comments, Facebook founder ordered his management team to only use Android phones - arguing that the operating system had far more users than Apple's, according to an investigative report by the Times.
"I wouldn't be in this situation", his pithy response was at the time.
Johnny Bobbitt arrested in Philadelphia, charges expected in GoFundMe case
Attorneys for Bobbitt tell FOX 29 they were informed by the defense team after the ruling that the money was gone. This story went viral last November when Kate McClure posted it on social media.
But Cook and Zuckerberg have traded barbs for years.
In the same interview and in subsequent speeches, Cook called for privacy regulation that would impact businesses like Facebook, which make their money from ads, significantly more than Apple, which makes money from hardware sales. Cook said in an interview with Charlie Rose in 2014 that "When an online service is free, you're not the customer".
Facebook, as part of its response to the Times piece, acknowledged that it has a policy of promoting usage of Android phones over Apple's iPhones. "You are oh great and powerful Zuck", replies a sultry Google Assistant, probably.
Zuckerberg is said to have justified the decision by saying more Facebook customers use Android than Apple.
What do you guys think? And just like that, he orders every Facebook worker to use Android phones.