I think it’s because he just didn’t fit in. Not quite a geek or a nerd, more of a socially awkward doofus. Kind of a square. That it wasn’t all that apparent is likely because he did have some depth to him, so maybe with that added dimension it would be more appropriate to call him a cube.
…
My guess: when a poster arrives and is unceremoniously banned after a handful of posts–particularly when that handful of posts seem pretty much in line with Board culture and whatnot–it was probably a sock.