Bears, mostly because of how incredibly loud/noisy they are.

Mages.

I.HATE.WARDS.

Ice wrasps!!!

There's a special niche in my player memory for hating spriggans. They've been a different sort of annoying in each game.

Bloodmoon: gotta kill every durned one three times.
Oblivion: curvaceous tree monster giggles while she attacks me. Devs must have thought that seemed sixy, but would have loved to see a toggle for "Shut up; I'm female and straight."
Skyrim: what High Heart said.

Draugr who use disarm shout.

Thankfully they grow out of that "phase"

Spriggans

I was just going to say that too. Having to run around looking for my weapon is bad enough. But then I have to re-favorite it and assign a hotkey to it all over again. *grrrr*

well the holes in the walls the falmer come out of are different from the automatons

Bears should be exterminated in video games!!!!!!!!! Seriously!!!!!!!! lol plus those Dragon Priest bastards!!!!!! I hate them!!!!!!!!

Mages that shoot icicles with perfect accuracy

Random dragons and bears for me. Bears are too plentiful and dragons... just attack already. I hate when they fly down and hit you once, then just never seem to return and you end up chasing them around for a while before giving up and just getting on with your business.

Nothing in Skyrim are as annoying as those bloody cliffracers from Morrowind lol

That said, i find wolves annoying, everytime have to dismount and fight them cause Lydia always wanted to fight them when we're travelling.
Solved my problem by making a friendly creatures mod and all is well

I love fighting dragons, don't know what you lot are smoking. Why has no one mention the f-ing WOLVES? Or mudcrabs? Really it's so annoying to aggro creatures that are so below you several times over. I'm 2-3 times your size. You should know I can kill you. Go away and eat a fox.

And with INFINITE F-ING MAGICKA TOO. Right? Ugh this *expletive* is annoying.

Those floaty guys found defending word walls. Dragon priests? They're so hard to catch or hit.

i like them all, I wish there was more of them especially the spiders, bigger, tougher, with fangs that can grab you and pump in the poison. I would love it if about 20-50 small spiders would burst out of the egg sacks and swarm you when walking past them. I could care less about the dragons killing npcs, I wish you could still aggro the npcs like Morrowind. I think they all should be harder to kill.

^that and Falmer Shadowmasters. I hate those SOBs.

1. Bears/Wolves/Sabre Cats.
2. Draugr with full Unreleting Force shout.
3. Dragons (Only sometimes, when are disturbing quests).

Trolls and Draugr. They're too resemblant to Ghouls and even more boring. Even if at first they may seem "cool". Falmer ShadowMasters and Forsworns Briarhearts too,but i love them too much

However, i usually avoid Bears and the other annoying animals cited here with "that shout"

Forsworn Briarhearts. They're just so darn difficult!

I play on Adept, so different people will have different experiences. As for myself...

Snowy Saber Cats, especially on low levels. 2 or 3 hits is all it takes, and it isn't fun when you've just traveled from Whiterun almost all the way to Winterhold and forgot to save -__-

I really hate Falmer. On their own, or a couple together, isn't too bad. But when 5+ swarm you and a couple are high level Falmer that use magic, it's over. I also never understood why they're able to shoot you accurately, aren't they blind? Chaurus are super annoying too, that poison kills fast.

ICE. WRAITHS. If you aren't a mage or assassin, these things can be a huge nuisance. I almost always get owned with my current sword/shield warrior against these things.

I second the ice wraith nomination.

Can't see [censored] when it's snowy, my character just blindly swings at air until I catch it.

I don't find bears that annoying cos' they're always so slow.

Flame atronachs, not difficult to kill at all, but when they explode after they are dead it makes me lose bowel control. Every...single...time.

Most of the wildlife. Kyne's peace ftw!

And random dragons, just when you are on your way somewhere (and are a bit short of healing potions...). After 200 or so hours I had my first case of two random dragons and a sabre cat yesterday. My character (with Vilkas in tow) was just on her way to meet Esbern and Delphine at Karthspire when they attacked. While fighting them, I came closer to Karthspire than I realised, and suddenly I saw this guy throwing fireballs at it - it took me a while (because the frigging dragons were everywhere) before I realised it was Esbern. He and Delphine killed one of the dragons, I had to sprint there to get the soul, and then suddenly there were Forsworns everywhere, attacking everything and everyone. And Vilkas got stuck somewhere further away, I'm not sure what he was fighting (wolves? Mudcrabs?) but I heard him happily yelling insults long after the dragons were dead. Very confusing (and actually quite fun - but I've reached the stage when I sigh and say "not AGAIN" every time I hear that distinctive dragonroar somewhere above me).