Tesla CEO Elon Musk unveiled Tesla’s first electric pickup truck, the Cybertruck, on Thursday, but things went wrong when the supposedly “bulletproof” windows of the truck shattered.

Musk asked his chief designer to throw a metal ball through the glass window, but was surprised when the ball broke the glass. The glass immediately cracked, drawing gasps from the crowd and an unhappy reaction from Musk. “Oh my f****** God,” he said onstage, “Well, maybe that was a little too hard.”

Musk, who previously claimed the Cybertruck’s was “literally bulletproof” to a 9mm handgun, had no explanation as to why the glass cracked. The Cybertruck, which Musk called, “the official truck of Mars” on Twitter, was quickly turned into a PR disaster. “We threw wrenches, we threw everything — we even literally threw the kitchen sink at the glass and it didn’t break,” Musk said. “For a little weird reason, it broke now. I don’t know why.”

Shares of Telsa have dropped 6.3 percent since Friday.