The spat began when Mr Unsworth ridiculed Mr Musk's effort in the rescue by having engineers at his companies, including Space X and The Boring Co., develop a mini-submarine that could transport the boys to safety. Unsworth, who had years of prior experience with the cave, advised authorities on the rescue effort. Unsworth said it was nothing more than a "PR stunt" and Musk could stick the contraption "where it hurts".
In his opening statement, Unsworth's lawyer, Taylor Wilson, said the tweet was more than a slip-up, and Musk had no business branding Unsworth a pedophile "in what should have been one of the proudest moments of his life".
Musk responded angrily on Twitter, vowing to demonstrate that the submarine could have squeezed through the tightest passages on the rescue route.
Calling Unsworth a "pedo guy" was not an allegation of pedophilia, but instead a "fill-in-the-blank insult", the attorney argued.
Musk's testimony will continue on Wednesday, when he will be questioned by his own attorney.
The Tesla boss apologised to the cave diver in court, looking directly at him and saying: "I apologised in a tweet and again in the deposition, and I'll say it again: I apologise to Mr Unsworth".More news: China wants tariff rollback for phase 1 trade deal
He also repeated his clients' claim that "pedo guy" was a common insult in South Africa, where Musk grew up.
They have also said Unsworth sought to profit from his role in the rescue and provoked Musk's response by suggesting on CNN that Musk did not care about the lives of the trapped boys.
Unsworth sued Musk in September 2018, two months after playing a leading role in the rescue of 12 boys and their soccer coach from the Tham Luang Nang Non cave.
"I knew he didn't literally mean to sodomize me with a submarine, just as I didn't literally mean he was a pedophile", Musk said.
Musk's lawyers have argued that the tweets were an opinion and not statements of fact, but it was later revealed that Musk hired a private investigator who was a convicted felon to investigate Unsworth who provided little evidence to back up Musk's claims about the cave diver.
He must prove the tweets were false, that Mr Musk did not use reasonable care to determine if they were true, and that people reasonably understood them to mean he was a paedophile. "I think that would have been worse".
Unsworth helped rescue a youth soccer team from a flooded cave in Thailand previous year.More news: Jaguar F-Type gets new style, fewer models
"I fucking hope he sues me", Musk wrote to the journalist.
Musk's lawyers were unsuccessful in their attempt to keep the email from the jury. But Mac, who hadn't agreed to keep the exchange confidential, published it anyway.
Mr Musk's attorney, Alex Spiro, said the lawsuit was over "joking, taunting tweets" in a fight between men.
Spiro also said Unsworth had not been harmed by Musk's statements, noting that the cave explorer had since been honored by Queen Elizabeth and Thailand's King Maha Vajiralongkorn, among others. He cast Unsworth as the aggressor in the pair's interactions, noting that the rescue was over and Musk had returned to the U.S. when Unsworth gave his interview to CNN.
"Just as I didn't literally mean he was a paedophile, I'm sure he didn't literally mean shoving a sub up my ass", Mr Musk testified, provoking snickers.
Musk's high profile has made it hard for the court to assemble an impartial jury.
One was due for a job interview at SpaceX.More news: Rugby Australia apologises to Israel Folau as settlement is reached
One woman said she had a strong feeling about billionaires and was dismissed.
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