The first-ever flying car conference got underway earlier this week in Dallas, a two-day affair put on by Uber called the “Uber Elevate Summit,” which was chock-full of panels and a big prediction: By 2020 Uber will be testing out its commuter aircraft. On Friday, Elon Musk seized another opportunity to shoot down the idea before it lifts off.

“I’m in favor of flying things,” Musk told interviewer Chris Anderson during his lengthy interview at the TED 2017 conference in Vancouver, before repeating a biting joke he first made in a February Bloomberg article.

“There is a challenge with flying cars in that they’ll be quite noisy, the wind-force generated will be very high,” Musk said. “Let’s just say that if something’s flying over your head, if there are a whole bunch of flying cars all over the place, that is not an anxiety-reducing situation.”

“You don’t think to yourself, ‘well, I feel better about today,’” Musk deadpanned to laughter in the audience. “You’re thinking, ‘did they service their hubcap? Or is it going to come off and guillotine me as they’re flying past?’”

Musk made the same joke back in February to Max Chafkin of Bloomberg:

“If somebody doesn’t maintain their flying car, it could drop a hubcap and guillotine you. Your anxiety level will not decrease as a result of things that weigh a lot buzzing around your head.”

The illustration that tops Uber's massive whitepaper on this flying car plan, released in October 2016.

It amounted to a thinly veiled burn on Uber, a company Musk has made a point to call out before. In October 2016, he characterized the embattled company’s suffering public reputation as “the people vs. Uber.”

While the ride-hailing/food delivering behemoth Uber isn’t exactly a direct competitor to Musk’s electric car company Tesla right now, it may one day find itself competing for customers. That’s because Musk has a plan for Teslas — which he said will achieve near-perfect autonomy using cameras and GPS in just two years — to be used as ride-sharing vehicles.

It’s an idea he first brought up in his “Master Plan, Part Deux” in July 2016: “You will also be able to add your car to the Tesla shared fleet just by tapping a button on the Tesla phone app and have it generate income for you while you’re at work or on vacation, significantly offsetting and at times potentially exceeding the monthly loan or lease cost.”

Uber surely took note of that projection from Musk, who on Friday was asked if he still thought the future of cars would mean more sharing. This was his reply:

“Absolutely this is what will happen,” he said. “There will be a shared autonomy fleet where you buy your car. You can choose to use that car exclusively; you can choose to have it be used only by friends and family; only by other drivers who are rated five-star; you can choose to share it sometimes but not others times; that’s 100 percent what will occur, it’s just a question of when.”

Between insults about flying hubcaps and indirect threats to their business, it doesn’t seem like relations between Musk and Tesla, and Uber, will warm up any time soon.