Elon Musk Sings Johnny Cash Around a Campfire

Elon Musk geeked out to Johnny Cash ... and he never looked cooler.

The brains behind Tesla and SpaceX sang along to "Ring of Fire" ... while firing up some s'mores with one hand and holding a cup 'O whiskey with the other. Elon's happy enough with his performance he posted it on Instagram.

Gotta say ... pretty awesome to see a super techy have some old school fun around a bonfire. If killer robots ever become a thing ... they'll know to look for him -- at camp.