So, I was thinking about Shouty's definition of artificial difficulty from the podcast (podcast to come this upcoming weekend because there's another bit I'd like to put in there). Just as a refresher, he said he considered artificial difficulty to be difficulty that was unintentional on the designer's part.
Certainly, this definition has merit. I don't think that definition falls in line with how I've heard the word used before, though. A lot of times, artificial difficulty refers to difficulty that's perceived as lazy on the developer's end. For instance, if you made enemy HP ridiculously high in a brawler, that would be considered artificial difficulty.
Notably, by this definition, knife-faces in Master of Darkness could be considered both a jerk move on the developer's part and artificial difficulty. On the other hand, it's interesting that this alternate definition still relies on caring what the developer did.
There's also a definition that implicitly came up twice. First, Soup said that the hawks were artificially difficult because they didn't fall into line with what the game had done before; the entire game was built around you learning enemy patterns, and then the hawks came along and made it impossible because you couldn't learn one standard attack pattern for that enemy. Then, Wariofan said that the maze was artificially difficult because you had gone from left to right the entire game and weren't expecting to have a maze to solve. While he admitted that this didn't quite match Shouty's definition, it did speak to another sense of artificial difficulty.
In both cases, artificial difficulty was implicitly defined as the game expecting something of the player without warning. The idea is that the game has a normal difficulty curve which gets disrupted. Some new element is introduced without regard for the difficulty curve which the game had already relied on. Rather than the developer, this definition either looks to the game itself or to the player's experience of the game--it could go either way, really.