Elon Musk embraced unorthodox designs for Tesla Inc.’s all-electric pickup to wow truck buyers and help differentiate it from popular gasoline-powered models that he knocked as boring look-alikes.

But the features he is promising could dent the commercial prospects of the vehicle Mr. Musk has dubbed Cybertruck.

Mr. Musk late Thursday unveiled the triangular, stainless-steel truck that evoked a science-fiction future. The unveiling outside Los Angeles focused on showing how robust the vehicle would be and how it would stand out from big sellers such as Ford Motor Co. ’s F-150 or General Motors Co. ’s Chevrolet Silverado and the GMC Sierra pickup family. The Tesla pickup is even bulletproof, Mr. Musk said.

But when it came to demonstrating the Cybertruck’s toughness, things went ominously off script. Mr. Musk asked his head of design to throw a small metal ball at the vehicle’s side window. The resulting crack of the window surprised the audience, including Mr. Musk.

“Oh my f-ing god,” Tesla’s chief said. “Maybe that was a little too hard.”