It's honestly not meant to be a bun, somebody just called it that earlier. It's just a shaved head with a bit of a messy ponytail in the back like this kid from Vikings...

[img]https://s-media-cache-ak0.pinimg.com/736x/9d/81/5b/9d815b17270629066870215a95a0ac4f.jpg[/img]

~KL~