Why don't gas pumps spark and explode?
photos here  In fact, they do spark and explode!

A sign that tells you how to to behave is the only obvious protection I can see, though maybe there's hidden stuff behind the scenes.  Personally, I think some sort of affordance that forces users to touch a grounded piece of metal before pumping would help a bunch.  In the olden days, we'd always have to flip some form of mechanical lever to enable the pump and reset the price tally from the person who pumped before us, so this is probably doable.

I think a flame detector in the pump handle that cut off the gas flow might prove useful, too.  The really bad accidents occur when the fumes flash over and somebody panics and removes the still-pumping handle.

At many of the gas stations I've used, they remove the clip that keeps the handle pressed down, so you're forced to hold on to the handle to keep pumping gas.  It puts an end to the messing around to build up static, but I don't like this approach.  Instead of making me hold down the handle, it just encourages me to use other gas stations that leave the retention clips in place.