Tesla's shares are tumbling before the market open Thursday after the electric vehicle maker posted a record first-quarter loss and its CEO got testy at times during a conference call.

Tesla tore through $745.3 million in cash in the quarter, due largely to the slow production ramp-up of the Model 3 mass-market electric sedan. When questioned on the Model 3 by an analyst, Elon Musk cut him off, calling questions dry and "not cool." He then allowed multiple questions from a person via YouTube.

RBC Capital Markets' Joseph Spak called it an "odd conference call that lacked answers to questions on investors' minds and overshadowed earnings."

"The general sentiment was that the defensiveness spoke volumes," he added in an analyst note.

Shares dropped more than 7 percent in premarket trading.