Smeags on 04 November 2012
Medusa Heads are incredibly annoying, especially when they're located in areas with spikes (since being hurt in stone form causes double damage... and falling into spikes already deals a lot of pain).
Sea Creepers from Resident Evil: Revelations are annoying as well (unless you have shock grenades). Nothing worse than two Sea Creepers in the same area without a Shock Grenade. Prepare to mash the Y button. 
Chilfos from The Legend of Zelda: Twilight Princess. That room full of them in Yeto's mansion was terrible.
