Someone who doesn't label themselves, especially in relation to political party, philosophy or religion, but could apply to other arenas where someone shuns a particular label. Of course the irony of being an antilabeltarian is that yet another label has been adopted.
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.