“Green Hills Software is a pile of trash,” the Tesla founder wrote on Twitter.

King not just of Tesla  (TSLA) – Get Tesla Inc Report but also of clapping back on Twitter  (TWTR) – Get Twitter, Inc. Report, Elon Musk called the software being used for some other electric vehicles “a pile of trash.”

The argument began when, on Sunday, Green Hills Software CEO Dan O’Dowd wrote that he had placed a full-page ad against Tesla’s Full Self-Driving (FSD) technology in The New York Times.

“Today I placed a full-page advertisement in the @nytimes, campaigning to ban @Tesla full self-driving from our roads,” O’Dowd, who founded Green Hills Software in the 1980s, wrote. “@RealDawnProject is organizing the opposition to @ElonMusk‘s ill-advised full self-driving robot car experiment.”

O’Dowd’s post was quickly called out by many as a publicity stunt meant to draw attention to the company. Along with making automation technology for the defense and airline industries, the Santa Barbara, Calif.-based Green Hills Software also creates software for electric cars. The company recently said that it was making the self-driving software for the BMW iX.

Responding half a day later, Musk called Green Hills’ product “a pile of trash” and wrote “indeed” under a comment claiming that the “most vocal critics of FSD always have a huge financial interest in a competing solution.”

“Linux ftw [for the win,]” Musk wrote underneath O’Dowd’s post.

O’Dowd claims that he started pressure group The Dawn Project and placed the advert to draw attention to “unsafe software from safety critical systems.”

Multiple auto industry experts have, in fact, criticized FSD’s tendency to glitch — in November, Tesla recalled over 10,000 electric cars after an update caused the brake system to activate without warning. That said, respondents under O’Dowd’s post claimed that he was latching onto this simply to sell his own product.

“I think it’s only fair and honest for you to disclose which Tesla competitors your company Green Hills Software have taken money from,” investing YouTube personality Dave Lee wrote on Twitter.

Not one to hold back what he thinks, Musk frequently starts and enflames existing Twitter spats. In November, he challenged UN food program director David Beasley’s claim that 2% of his wealth would solve world hunger definitively. When Beasley responded with a 1,000-word summary of where the money would go, Musk started demonstratively dropping his Tesla shares.

When Massachusetts Senator Elizabeth Warren (D-Mass.) wrote that mega-billionaires like Musk should perhaps pay more in taxes, he told her to “stop projecting” and called her “Senator Karen” on Twitter.