Imagine that you know the laws of thermodynamics. Not just know them, but you're constantly aware that everything you do, right down to breathing, contributes in some way to the heat death of the universe. In a closed system, energy has nowhere to go except gradually become useless in the form of waste heat. That's entropy - all energy is landlocked in heat.
So what wastes more energy - trying to impose order on the universe, which takes a lot of doing (see government, organized religion and history), or giving up and not even obeying one of the few rules you apply to your self, namely not eating hot dogs on Fridays? Since trying to impose order on a universe that appears, from a scientific standpoint, to be habitually chaotic, only makes the universe more chaotic, it could be argued that organized religion does more harm than good. Consequently there's no point in trying to save the universe.Rather than waste their time saving it, Discordians do their best to put the universe out of its misery.
The Principia Discordia, when you read it with this in mind, makes more sense - disturbingly enough. In making a parody of organized religion it describes the uselessness of said establishments. In establishing rules that contradict themselves it describes the whole point of Discordianism - namely not wasting energy on rules, because they are futile. In worshipping Eris, Discordian thought works much like monotheistic religions - worshipping a symbol of the ideal that is truly held up on the pedestal. Where monotheists traditionally worship the concept of order and a Divine Plan as symbolized by an all-seeing God who put everything out for a purpose, Discordians embrace the concept that the universe is slowly dying and pull a Kevorkian on it, a mercy killing, by working towards Entropy rather than away from it in vain. They do this through worship of Eris, goddess of discord.
Updated:
To clarify a little more: You can create more chaos on purpose than when you don't mean to. Organized religion is a waste of time, but Erisians still hold to a religion - its just that the founding principle of their religion is disorder. So its a disorganized religion - by putting out the Principia and being contradictory to everything, including themselves, they don't just look funny, they are constantly perfoming the equivalent of a Eucharist - reminding themselves of the core concept of Discordianism. This is as close to a ritual as Erisians will get, but its all too effective.
Doesn't seem like such a big joke anymore, does it?
Interestingly enough, from this viewpoint Discordianism is directly contradictory to every last commonly accepted social value known to man. The book of Revelation was written in code so that only Christians would understand it - the Romans would think of it as garbage. Take this in mind when you read the Principia Discordia next time - and keep in mind that its really only published by one company, and it also makes games - they print the Principia because they think its funny, too.