Wet willies are the toddler precursor to swirlies and wedgies. If pranks were insects, this one is the mosquito of the prank world.

Some devillish youth licks his finger and leaves it sloppy. Then, when someone least expects it, he plunges toward the unsuspecting person's ear, and drives his sopping wet finger home. Most often accompanied by a shrill scream and instant covering of the ears.