About US$13bn (€11.7bn) was wiped off Tesla's shares after chief executive Elon Musk tweeted that the electric car company's "stock price is too high".
In a series of other tweets, Mr Musk (48) also said he was "selling almost all physical possessions" and "will own no house".
He added his girlfriend was "mad at me".
The subsequent 9% drop in Tesla share prices erased about US$3bn (€2.7bn) from Mr Musk's own stake.
Nevertheless, they remain almost 50% up from the start of April.
The Wall Street Journal said Mr Musk responded to an e-mail asking whether he was joking, or whether his tweet was vetted, by saying: "No."
It is not the first time Mr Musk has sent provocative tweets.
In April 2019, he posted: "My Twitter is pretty much complete nonsense at this point."
In August 2018, he tweeted that he had secured funding to possibly take Tesla private.
It led to a fraud case by the US Securities and Exchange Commission (SEC), which Mr Musk settled by agreeing to pay US$20m (€18.1m) and have a Tesla lawyer pre-screen tweets with important information about the company.
The latest posts on social media are not the only controversy Mr Musk has found himself in this week.
He described coronavirus lockdowns as "forcibly imprisoning people in their homes" and "fascist".
Mr Musk said he did not know when Tesla could resume production in California - and called the state's stay-at-home order a "serious risk" to the business.
He added: "To say that they cannot leave their house and they will be arrested if they do, this is fascist.
"This is not democratic, this is not freedom. Give people back their goddamn freedom!"