There's a difference between an in-joke and a meme. An in-joke doesn't have to be funny; it is merely a vehicle to foster a bond forged from shared experiences, which is one of very few things you can bond with via an anonymous forum. If you think that's shallow, then maybe it is - but so is any social behavior when stripped of everything but its core purpose. So enjoy it. Or let other people enjoy it, and don't be mad when they do.