I guess he is a messenger whose boss wants him to wear a helmet, so he carries one to put on when he goes to base. A leather hairnet would be a great way to thumb nose at boss like those flimsy motorcycle helmets worn by 1%ers to get past helmet laws. I carry a Giro, and I carry it on my head to keep my hands free and more space in my bag. Also if I fall on my head which happens about once a decade, it hurts less.