the result of a drunken night of shameless sex involving a soldering iron, anal eaze, hand-cuffs, a gerbil, ice cubes, and of course candles(to set the mood).
A sunburn or suntan focused on the left arm. It is caused by the left side of the body being the only half that gets exposed to sunlight while driving. Presumably, it would be located on the right side of the body in countries where they drive on the left side of the road.