If a friend has been grumpy lately, cheer them up with this delightfully harmless (and funny) prank. Take six different colors of acyrlic tube paint. Red, orange, yellow, green, blue & purple always work nicely. Put a small dab on the windshield just above the wiper blade. Once the wiper is engaged a rainbow will be painted across their windshield. In desperate situations, a double rainbow may be necessary.