What are the most annoying bosses you've encountered in video games? Not necessarily hard, just annoying.
Grapple Guardian from Metroid Prime 2: Echoes is probably this for me. It isn't as hard as say, Boost Guardian, but just trying to hit it can be an ordeal and the fight goes on for far too long.
-
Sundowner from Metal Gear Rising gave me a run for my money. The accuracy of your slices need to be perfect, but the cone needs to be worked on so you are not a milifraction off.