Chief executives are being warned to “think twice before they tweet” after the boss of takeaway company Just Eat Takeaway was told his Twitter spat with Uber threatened to undermine the firm’s reputation. Jitse Groen this week became the latest in a growing list of chief executives to be rebuked by customers, investors and even regulators over ill-judged tweets. Cat Rock Capital Management, an activist investor which has a 4.7% stake in Just Eat, highlighted Groen’s Twitter battle with Uber boss Dara Khosrowshahi as an example of outbursts that damaged the brand. The investor said Groen’s tweets had partly led to the firm being “deeply undervalued and vulnerable to takeover bids at far below its intrinsic value”. Earlier this year Groen had a rant at financial analysts on Twitter, claiming that “some can’t even do basic maths”. He tweeted that he was “amazed how bad these analysts have become … All of them mix up definitions. It’s unbelievable.” Brand and marketing expert Mark Borkowski said Groen’s case highlighted the difficulty executives face when trying to engage with customers on the platform. “Everyone sees Twitter as a huge marketing opportunity that can drive a business forward, and it really can,” Borkowski said. “But these bosses must stop and think twice before they tweet, as just one misjudged tweet can send their share price plunging.” Possibly the most expensive tweets ever sent were posted by Elon Musk, the maverick boss of electric car company Tesla, in 2018. The US Securities and Exchange Commission fined Musk and Tesla $20m each after he tweeted that he had “funding secured” to take the company private at $420 a share. The regulator said the tweet, which sent Tesla’s share price up by as much as 13%, violated securities law. As part of the settlement, Musk was ordered to step down as Tesla’s chairman. Musk’s tweets continued to anger some investors. Pirc, an influential adviser to shareholders including the UK’s local authority pension funds, last year recommended that investors voted against Musk’s re-election to the Tesla board because his tweets posed “a serious risk of reputational harm to the company and its shareholders”. This week, he responded to Boris Johnson’s proposal to create “fluorescent-jacketed chain gangs” of people found guilty of antisocial behaviour with a tweet suggesting offenders should be helped into work instead. Tim Cook, the chief executive of Apple, has won praise for using Twitter to successfully pressure the governor of Indiana into revising proposed legislation that had threatened to allow discrimination against gay people on religious grounds. Researchers at Harvard Business School and Duke University said Cook “effectively framed the debate using social media at a time when opinions were being formed and the impact went beyond the political”. Borkowski suggested that before chief executives tweet they should “consider whether they have the personality and temperament to get the tone right each time”. “There is nothing more inelegant than a chief executive going after rivals publicly on Twitter,” he said. It was exactly that sort of behaviour that Cat Rock had accused Groen of undertaking. When Uber Eats announced earlier this year that it would take on Just Eat in Germany, Groen lashed out in a tweet directed at Khosrowshahi, accusing him of “trying to depress our share price”. Khosrowshahi replied that perhaps Groen should “pay a little less attention to your short term stock price and more attention to your Tech and Ops”. That sparked Groen to reply “thank you for the advice, and then if I may .. Start paying taxes, minimum wage and social security premiums before giving a founder advice on how he should run his business”. Alex Captain, Cat Rock’s founder, said: “The response should not happen on Twitter. It should happen on a credible forum with the facts, data, and analysis that the company has at its disposal.” A Just Eat spokesperson said: “Just Eat Takeaway.com has a regular dialogue with all its shareholders and we take all their views very seriously.”