A huge static charge can build up on plastic gas cans. A study was done several years ago where they measured the charge generated by the movement of the gas against the jug while filling and found 10's of thousands of volts. They stored the jugs inside with gas still in them for about 2 weeks and found the charge had not diminished. They found the best way to discharge the voltage was to wipe down the jug with a wet cotton cloth.
I became a real believer when I filled jugs for my plane and as I carried jugs back to my pickup I could feel the hair on my legs stand out.