Tesla and SpaceX chief Elon Musk is known to take on questioning investors, reporters and analysts, often around the clock, on Twitter.
But when Musk labelled a British diver who helped rescue 12 young Thai soccer players and their coach from a dangerous, flooded cave a 'pedophile' in front of his 22.2 million Twitter followers, he may have gone one tweet too far.
The deleted Thai cave tweet has sent investors fleeing from Tesla stock and could bring on a defamation case against the tech entrepreneur if the diver decides to pursue one.
"This has nothing to do with defending Tesla," Erik Gordon, a business and law professor at the University of Michigan, said.
"This goes over a line where he can't claim 'Well, my big sin is that I go too far in defending the company."'
It all started when British diver Vern Unsworth, in a television interview, criticised Musk for sending a mini-sub to help divers rescue the Wild Boars soccer team, writing it if as nothing more than a "PR stunt". Unsworth said the sub would never have worked in the cave's tough, narrow conditions.
Musk hit back with a tweet branding Unsworth a "pedo" and said Unsworth's claim that the sub wouldn't work was not true.
Unsworth has told CNN he is considering legal action.
A Tesla spokeswoman wouldn't comment on the tweets.
For the first four months of this year Musk has averaged around 100 tweets per month, but that figure spiked to 400 a month from May as Musk came under pressure to increase production of his lower priced Tesla electric car.
Musk gained thousands of extra Twitter followers at this time, almost half as many as US President Donald Trump, who also likes to attacks his critics on the platform.
Hedge fund manager Mark Spiegel, who has been betting on Tesla's stock falling for years, said the tweets show Musk's true personality.
The company, which has had only two profitable quarters, is deep in debt and will have trouble meeting Musk's prediction of a profit in the second half of this year, Spiegel said.
"It's all based around this rabid Elon Musk fan base. Once that fan base starts to see what kind of person they've been worshipping, they will turn on you on a dime," he said.
Spiegel likened Musk to Trump, saying the two men have an "amazing amount of personality defects in common."
Previous comparisons with Trump have angered Musk.
Earlier this year Andrew J. Hawkins tweeted that Musk was transforming into a "media-baiting Trump figure screaming irrationally about fake news."
Musk responded by lashing out at the media for the Trump comparisons, writing: "Why do you think he got elected in the first place? Because no one believes you any more."
In his defence, Musk posted on Twitter that leaders of the Thai rescue, in which all the boys and their coach were safely extracted, had asked him to build the mini-sub.
Tesla stock fell nearly three per cent on Monday to $US310.10 even though the broader market was up slightly.
