Even if billionaire Elon Musk ever decides to pack it in as CEO of SpaceX and Tesla, he can point to his success as a pitchman for flamethrowers.

Tonight he declared that his planned inventory of 20,000 fire-spitting guns was sold out, just four days after the sale opened on the Boring Company’s website.

At $500 a pop, that means he’s grossed $10 million for the company, whose main purpose is to lower the cost of excavation and open the way for high-speed transit tunnels.

But wait … there’s more: Musk said every buyer would get a free fire extinguisher, which was going for $30 extra when the sale began on Saturday.

Flamethrowers sold out — Elon Musk (@elonmusk) February 1, 2018

All flamethrowers will ship with a complimentary boring fire extinguisher — Elon Musk (@elonmusk) February 1, 2018

Is it just an early April Fool’s stunt? Twenty thousand buyers hope not, although it’s true that the flamethrowers — which appear to be converted air guns — are due to start shipping in spring.

Another slightly suspicious sign is this Boring Company caveat: “Before shipping, aspiring flamethrower aficionados will be sent a terms and conditions rhyme for review and acceptance.”

The website also says the flamethrowers “may not be used on Boring Company decorative lacquered hay bales or Boring Company dockside munitions warehouses.”

That sounds like a dealbreaker to me.

Musk certainly made hay out of the sale, which traces its origins to a tweet in which he promised to offer flamethrowers if the Boring Company sold 50,000 of its $20 logo hats. Here are some of the tweets that Musk used in his sales pitch:

When the zombie apocalypse happens, you’ll be glad you bought a flamethrower. Works against hordes of the undead or your money back! — Elon Musk (@elonmusk) January 28, 2018

The rumor that I’m secretly creating a zombie apocalypse to generate demand for flamethrowers is completely false — Elon Musk (@elonmusk) January 28, 2018

You’d need millions of zombies for a so-called “apocalypse” anyway. Where would I even get a factory big enough to make so many!? — Elon Musk (@elonmusk) January 28, 2018

Musk even temporarily changed his Twitter bio to “Zombie Defender” to match the theme.

Running around with a flamethrower sounds like a teenager’s dream — or a parent’s nightmare. The 46-year-old father of five insists that the Boring Company version will be safer than a steak knife, spewing a flame no farther than 10 feet. Flamethrowers aren’t federally regulated, but California law requires a permit for devices that throw flames 10 feet or more.

After the flamethrower sale began, Miguel Santiago, a California state lawmaker, said he was outraged by Musk’s gambit, particularly since it was coming in the wake of a devastating wildfire season. He promised to introduce legislation to block the sale. “NOT FUNNY,” Santiago tweeted. “NOT GONNA HAPPEN.”

It could be a couple of months before we start seeing user reviews of the darn things, or any sort of regulatory action, or any admission that the whole thing was a joke. In the meantime, Musk has more than enough to occupy his attention.

The test flights of SpaceX’s Falcon Heavy rocket, the ramp-up of production for Tesla’s Model 3 electric car and the work on other Tesla products such as the Semi and the Model Y will surely rule out another wild-hair sales idea.

But let’s not give him any ideas … oops, too late:

Any chance of selling snowthrowers because it’s hot as F in Australia — Andrew Hobden (@AndrewGHobden) February 1, 2018