Say what you will about X, but it’s still the best place to watch powerful people slam each other on social media. Elon Musk walked into an unsuspecting Twitter beef this holiday weekend with none other than Meta’s Chief AI Scientist Yann LeCun, who used the platform against the billionaire that owns it.

“[Musk] claims to want a ‘maximally rigorous pursuit of the truth’ but spews crazy-ass conspiracy theories on his own social platform,” LeCun said in a tweet Monday, responding to a job posting for a position with xAI. He mockingly listed other claims from Elon Musk, including that AI will kill everyone and the billionaire’s belief that xAI’s work will be solved next year.

“I like his cars, his rockets, his solar panels, and his satellite network,” LeCun said in a followup tweet. “I very much dislike his vengeful politics, his conspiracy theories, and his hype.”

LeCun clarified to another account that he is a scientist and not a business or product person. Musk chimed in to say LeCun was “just following orders,” to which LeCun said, “You don’t seem to understand how research works.” Musk responded by asking what ‘science’ LeCun had done recently, to which Meta’s Chief AI Scientist posted a link to his Google Scholar page with “over 80 technical papers published since January 2022.” The owner of X followed up by saying that was “nothing” and that LeCun was “going soft.”

The entire exchange, which LeCun later remarked as “holiday fun,” seemed slightly more hostile than either suggested. This followed a barrage of attacks from Musk against Meta’s products and services. WhatsApp is the latest victim of Musk’s tweet storm. He posted on Friday that the encrypted messaging app “exports your user data every night.” The head of WhatsApp responded directly to Musk saying, “This is not correct” and that the company takes security seriously.

Hugging Face CEO Clem Delangue said he would pick LeCun over Musk “every single day of the week.” Delangue noted that LeCun has made significant contributions to the AI community without cashing out like some others have. Notably, Musk’s X just announced a $6 billion funding round from a slew of Silicon Valley venture capital firms and investors.

The exchange also exposed a riff between Musk and LeCun’s views on artificial intelligence. Whereas Musk often preaches to AI doomers, those who believe the technology could be existential to humanity, LeCun offers a much less fear-inducing view on AI risk. LeCun calls these “doomers” delusional, and said in a tweet recently that “it’s too early to worry about [AI]. And it’s way too early to regulate it to prevent “existential risks.”