I didn't notice at first, but there is a problem. Not sex specifically, but the asymmetry. In the photo as well as in the text, the all too familiar "male over female" pattern showed all over.
Now if it were a female hacker talking the same talk and showing the same photo, only with her banging her boyfriend from behind, then it would be different, because this situation definitely isn't the default. It could still be offensive, but I would find it funnier.
I would go so far as to say it is pornographic. I don't have a personal problem with the style, but degradation as humor has never been a good enough excuse, in my household, anyway. I just sort of pity the kind of thinking that begets such accoutrements.
This is one of the worst trolls i've seen on HN. Obvious ignorance of pegging, flame-baiting the downvoters and trying to link the possibility of alternative sex acts with physics.
She could bang him with her fist too. That would be from behind, and completely feasible with human anatomy. Clearly you haven't been on the internet very long. I can probably find you video evidence in about 20 minutes...
Now if it were a female hacker talking the same talk and showing the same photo, only with her banging her boyfriend from behind, then it would be different, because this situation definitely isn't the default. It could still be offensive, but I would find it funnier.