Oh yeah, the undead (gibdos or something like that?) from every every recent Zelda. They scream when you get to close, which freezes the game for a second.  Then they grab onto you, and they can't be killed! You can knock them out, but to do so you have to suffer through the scream first.

the smb 3 evil sun

and don flamingo from punch out. f that guy.

The Wasp's/Bee's of Donkey Kong Country....

I hate the Minjos in Banjo-Tooie, especially if they're near lava or a poison lake or something like that. These fake Jinjos charge at you and push you off the ledge. Not difficult to beat, but they're still annoying.

I also hate the Medusa Heads in the original Castlevania.

the big headed guy in crash bandicoot, i wanna rip his puiny balls off

 Me too !! .. i hate those damn bees .... man that game was SO GOOD.

I know the answer to this question, and once I tell you about this particular enemy I feel certain you will agree entirely once you dwell upon it. This particular enemy knows no console boundaries, no genre boundaries, and no game boundaries. He can kill your character instantly, and he always has you under his finger turning up the pressure. He is a returning nightmare, and rest assured he will visit you even in a game where you think your completely safe from him.

I am talking about the dreaded, infamous, and ever ludicrous countdown timer. Your completely at its mercy, and defeating it which is often a matter of sheer will power rather then intellectual excellence feels less like a victory and more a narrow escape. Your only wanting to get away from it.

You all know what I am talking about there you are playing your game happy as can be. Then all of the sudden a timer appears, and the illusion is shattered now your expected to perform, and its rarely entirely clear what it is, or how to exactly do it. Then to add to your woes with that clock breathing down your neck, oh your going to screw up take a risk, because your timing is blown. Then more often then not your going to have to run this gauntlet eight, nine, or a hundred times. The countdown clock is like the least forgiving foe.

The most annoying time in just about any game imaginable is when a timer flies up on the screen. From that moment on you know your in for pain. There is no trial or error just trial and failure. No time for strategy beyond learning from what screwed you up the last time through. Just so you can get a little further to screw up again.

We have all faced him, and I guarantee every single player on these forums has had words with him. Cursed him out viciously, and flung controllers in outrage. Think back to all the times you were filled with vehement rage while playing a game, and I guarantee you that he has been behind a great many of them.

For those that are curious the runner up is the soft target in the escort mission, and yes he is your enemy too. You have to fight against his utter lack of skill. Confession time how many people would gun down the escort if it let them skip those levels. Hold up not everyone raise their hands at once.

These spiders in Phantasy star online (on gamecube episode one... in Ruins 2-3 i think)

the goombas in any mario's gamee o.0

Angels and Archers in the final dungeon of Tales of Destiny 2 (JP). The archers keep on shooting you when you are trying to attack the front line enemy and the angels and their spells are just annoying, 'nuff said.