Savato on Trauma Centre: Under the Knife.
Gargh.
How about Trauma Center: UTK, every single damn mission? Seriously, the game's pretty ridiculous overall. I'm still stuck on the second anyeurism operation...
Also, I'd like to add the Deftera from Trauma Center: Second Opinion. Good sweet buttery Jesus did those little guys give me hell. This coming from someone who can get an "S" operation rating on Hard-Mode Savato.