Dwarf Fortress. It's always broken, and historically has an interface style that most people don't get. It's also the masterpiece of a reclusive genius, and is a simulation so deep it has to be explained in parables, like the drunken cats one.
And, because every drink of alcohol was assumed to be one cup worth in some throwaway bit of code, and cats are small, they got massive alcohol poisoning and almost instantly puked themselves to death.
So, bug. The observed behavior was cat corpses and cat vomit accumulating in bars. The expected behavior was... not. Eventually Tarn managed to figure it out, and it was fixed by better modeling of the volume of just a layer of liquid on a body part. You also can't suck stuff off yourself to quench thirst in adventure mode anymore.
Lol, do you have a link? Off the top of my head I'm not sure how you'd do that, mod-wise, since dwarves only do fairly undirected violence when unhappy right now. (Insurgencies will be in a future version, eventually, just like everything else)
I mean, I enjoy it, but usually games are supposed to just work. Most of the difficulty of DF, at least historically, comes from trying to work around the hard edges and broken bits. Adventure mode is also pretty aimless and depressing, and Legends mode isn't even really a game.
I'd break it down in more detail, but I'm not really a great video game designer either. Most other people certainly agree that it's not very good as a game. Tarn even has said things to that effect.