Tesla stock faltered Monday after Chairman Elon Musk’s controversial tweets reached a new level over the weekend as he lashed out at a critic and called him a pedophile.

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Musk’s now-deleted post on Twitter came after British cave explorer Vern Unsworth blasted Musk’s effort to help rescue 12 boys from a Thai cave last week. It adds to a long list of news-making tweets by the Tesla (TSLA) chief.

Tesla stock lost 2.8% to close at 310.10 on the stock market today.

Musk offered a “kid-size submarine” to help rescue the boys and their coach after they became trapped in a cave in northern Thailand. A Thai official said the equipment, built by Musk’s Space Exploration Technologies, or SpaceX, wasn’t practical and it wasn’t used. Musk traveled to the site in Chiang Rai province, but the team was rescued by Thai divers with aid from an international group of volunteers.

Unsworth was a volunteer who played a key role in organizing the rescue. He said in an interview Friday with CNN that the submarine was “a PR stunt.” Unsworth said Musk could “stick his submarine where it hurts.” He added that it had “absolutely no chance of working.”

‘This British expat guy’

Over the weekend, Musk fired back in a series of tweets, without specifically naming Unsworth. The Tesla boss said he hadn’t seen “this British expat guy” in the caves during the rescue. He said he saw only Thai military divers. Musk also said he would make a video to prove that the minisub could have helped in the rescue.

“Sorry pedo guy, you really did ask for it,” he wrote.

Unsworth, asked about the tweets in a television interview, declined to say what he thought of Musk’s comments.

“I’m not going to make any further comment about him, but I think people realize what sort of guy he is,” he said. “It’s not finished.”

Unlike most executives, Musk doesn’t hesitate to battle publicly with his detractors. He uses the social network to promote his companies and spar with short sellers who are betting against Tesla shares. He also needles journalists who question his businesses’ prospects.

Musk has 22.3 million followers on Twitter.