For me, it depends on what game we're talking about, sort of, because it all constitutes a different kind of hard. For example, when I played Soul Calibur III, I was stupid enough to try and fight Night Terror at the highest difficulty. He's already a cheap fighter, having retarded amounts of range, power and speed, but upping the AI was nuts. Even on easy, I've had times where he's pulled a fast one and I lost.
As for RPG bosses... Dr. Lugae on FFIV DS. I can never manage to act in time with that stupid Reversal Gas, and I always end up hurting someone when I'm trying to heal them. I had no problem fighting him on ANY other system but this one, even when it wasn't dumbed down. IRRITATING as all Hell.
