Many years ago I was flying a Bell 206 in some Godforsaken part of the world and parked up at a small strip for refuel and overnight parking. I was filling in the tech log when I looked up to see the refueller pumping fuel out of a barrel marked AVGAS. As I was unsure about the effects and I was flying mostly over primary jungle I spent the night draining it out of the tank using a long screwdriver wedged against the sump drain and a marker cone. Every hour or so I would rouse myself and empty the cone.
When I told the Chief Engineer he laughed and said that I should have got a good nights sleep as it would have been perfectly OK to fly it back using AVGAS.