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.