Then, they all come home at the end of the day, and the kitchen is a disaster. Who's to blame?
Answer: You're to blame, because you're the only one left who gives a shit. Remember how I said there were four roommates? You're the fourth one. Ha! That's why they call it a riddle, you stupid fucking shitlord. Unless you actually got it, in which case ... well played, sir or madam, well played indeed. It is refreshing to encounter such a worthy adversary.
As Krogag would say, "I hope to one day meet you on the field of battle and make your wife a widow."
I'm gonna be straight with y'all: I am one mediocre-ass roommate when it comes to cleanliness. But I've lived in a lot of group homes and occupied every slot on the cleanest-to-grossest-roommate spectrum, and I can say with certainty that figuring out who's "to blame" is a complete fucking waste of time, because there is no right way to live. Look, fuckers, I got science: everyone likes their living space different. While some people can't even think unless it's cyborgs-have-taken-over-dystopian-future-level immaculate, others gain energy from the squalid hell-pit they call a home, like a sack of spider eggs feasting on human brain-juice. Living with another person isn't about enforcing your rules on them; it's about figuring out how to cohabitate. And if you can't agree about how best to do that, just figure out how to compromise until you can move out.