In September 2016, SpaceX was testing its Falcon 9 rocket at a launch site in Cape Canaveral, Florida. Shortly after 9 a.m. the rocket exploded, destroying Facebook's AMOS-6 satellite, which was supposed to ride the rocket into space.The satellite was part of Facebook's Internet.org project to deliver internet connectivity to the developing world and would have been Facebook's first satellite in orbit. Zuckerberg seemed openly frustrated that the launch failed, writing on Facebook that he was deeply disappointed to hear that SpaceX's launch failure destroyed our satellite that would have provided connectivity to so many entrepreneurs and everyone else across the continent.Two years later, Musk addressed the failed launch in a tweet to reporter Kerry Flynn.Yeah, my fault for being an idiot, Musk said. We did give them a free launch to make up for it and I think they had some insurance.During a Facebook Live broadcast, a viewer asked Zuckerberg for his thoughts on Musk's anxieties around AI. I have pretty strong opinions on this, Zuckerberg said. With AI especially, I'm really optimistic, and I think that people who are naysayers and try to drum up these doomsday scenarios ... I don't understand it. It's really negative, and in some ways, I actually think it's pretty irresponsible.Musk, who has repeatedly called for regulation and caution when it comes to new AI technology, shot back on Twitter.I've talked to Mark about this, he said in response to a tweet about Zuckerberg's comments. His understanding of the subject is limited. After WhatsApp cofounder Brian Acton tweeted, It is time. #deletefacebook, Musk responded, What's Facebook?A fan responded to Musk's tweet asking if he would delete the SpaceX Facebook page, to which Musk responded, I didn't realize there was one. Will do. After another fan pointed out that Tesla had a Facebook page too, Musk tweeted that it looks lame anyway.Soon after, both the SpaceX and Tesla pages disappeared from Facebook, but Musk said it wasn't a political statement, he just finds Facebook unsettling.In response to a tweet from the actor Sacha Baron Cohen, which called for more regulation of Facebook, Musk urged people once again to delete the app. On the evening of the rampage in Washington, Musk tweeted This is called the domino effect along with an image of dominoes, with the first one labeled a website to rate women on campus, a reference to Facebook's inception at Harvard University. The last domino was about the rioters. Musk also criticized Facebook's data-sharing practices, tweeting another meme about Facebook that mentioned the company spying on users following the announcement by Facebook-owned WhatsApp that it would start forcing users to share their personal data with Facebook.Musk tweeted that people should use Signal, an encrypted messaging app. His tweet was retweeted by Twitter CEO Jack Dorsey, another tech executive who has sparred with Zuckerberg.