Van der Graaf (pie pans)

'The charge on the Van der Graaf generator is used to charge up the thin aluminum plates. Each plate gets the same sign of charge and therefore repels the other plates ("opposites attract, like-signs repel"). The same effect happens if you touch the Van der Graaf generator yourself. All of your hairs will repel each other, and if they are long and clean and not tied down, they will all stand on end, as far away from each other as possible.'--http://van.physics.illinois.edu/qa/listing.php?id=2288

The same change in charges occures to the plastic hairs taped to the VdG generator, causeing them to stand on end.