Last winter I saw a clip on facebook about a woman who decorated a car with markers. Markers are easy enough to use and fun! However, the result seem to fade fairly quickly, and then you have to redraw it or scrub it of using an appropriate solvent. Let me tell you, it's a bigger and lot less fun job than getting it on there in the first place.
I filmed two of my drawing sessions this summer and a few hours of work resulted in 1 minute of film and a few months of decoration.
This movie also features my sunburned arm. Someone wasn't aware that bringing sun block with you in your bag is not in itself sufficient.