Never one to turn his back on a potential Twitter fight, Musk fired back, making a thinking-face-emoji insinuation about why Unsworth never sued him, despite being offered free legal services.
"Your dedication to facts and truth would have been wonderful if applied to that time when you called someone a pedo", posted Drew Olanoff.
"I think sometimes people think I spend a lot of time in Twitter", he told the YouTuber Marques Brownlee earlier this month.
When contacted by Sky News about the renewed controversy, Unsworth said, "It's all being dealt with, that's all I can say".
Musk responded in a since-removed tweet: "We will make one of the mini-sub/pod going all the way to Cave 5 no problemo".
"Have you actually done any research at all?" he said.
In a tweet to his 22.3m followers, Musk said: "Sorry pedo guy, you really did ask for it".
Musk is known for being unusually candid on Twitter compared to other CEOs, but he has become increasingly combative on the site this year, lashing out at critics and reporters and spurring questions about his judgment when using the site.
But everything was reignited on Tuesday, when ― after saying he totally, definitely, for sure didn't cry during a recent New York Times interview ― Musk further attacked Unsworth, suggesting it was true that he's a pedophile because he hadn't tried to sue.
Musk's freakish allegation came after Unsworth accused Musk of using the Thai cave rescue ordeal to stage a publicity stunt.
Musk said on Friday that Tesla would remain public, but said he believed there was "more than enough funding" to take the company private.
"Conventional business leaders are far more careful in their behaviour - you don't find FTSE 100 chief executives shooting from the hip like this because they are advised it would be detrimental to the interests of their companies", Matthew Gwyther, ex-editor of Management Today, told the BBC.