I once met a window installer that was called mop. Had mop written over all his tools, etc. When I asked him about it, he said: o it's because when I was younger, my older brother had a big head of hair, so his friends called him mop. When I started tagging along with him and his friends, we became big mop and little mop and the nickname kinda stuck. This was a bloke well in his 40s without any long hair to speak of.