Nerd porn baffles and scares me

I can understand nerds getting off to stuff that involves, you know, the opposite gender. However, I know from seeing this image that some nerd out there fapped to this image that had no female person/creature in it at all. That disturbs me. A lot.

I mean, what is this I don't even

ZOMG non-porn porn!

 Spoiler

and ninja-ing the best comment about this picture: "Those twenties are natural".