Like many pieces of modern internet culture, this image has been detached from its real source and context, and propagated memetically through the various social media platforms.
It doesn't seem like the large majority of the HN audience would participate in this, so it's still a bit weird to assume other readers would know the reference.
The large majority of the HN audience wouldn't participate in social media? I'm not sure what dividing line you're trying to draw here.
Communication is always in part a game of references. They are a form of compression of larger and more specific ideas, and of humor, which itself is a primary vector of communication.
I'm not sure what demographic I'd belong to, but I understood the reference just fine, and it seems like many of the other participants in the thread did too.
I'm sure you've got references that I'd miss completely, that you believe to be obvious.