Tekken 5 - Jinpachi. He does double the damage, and has a fucking fireball attack that drains like 80% of your health and then stuns you so he can kindly finish shoving his foot up your ass. Azazel is even worse.
Prince of Persia - The Two Thrones ... I don't know where to begin. Well, the Twin Bosses where a ***** to fight ... also, in the middle tower, there is a bugged wooden springboard that shoots you not where you're supposed to go. I've died at least 20 times before I got lucky and exploited the glitch >
Assassin's Creed Brotherhood - Some of the requirement are ridiculously hard ... the one that comes to mind is one of the Da Vinci Disappearance mission where I have to tackle a courier. Problem is, there are 3 groups of guards in my way, and if I dodge them, the courier is lost. If I summon my assassin minions, they kill the courier and the mission is failed. In the end I got lucky tackled that ************
Duke Nukem Forever - The second time facing the Machine gun giant boss (The Overlord I think). It's so frustrating running around to get to cover only to have the boss destroy the cover. And on top of that he has 2 lives, so when I finally killed him the first time and he got back up I died. I was so angry I stopped playing the game ... yep, 12 years just to have the game piss me of
And last but not least - The Witcher 2's Final Boss fight ...