I'd say Watchhog from the trainers.

They always Hynosis followed by Super Fang.

Hynosis supposed to  have 60% hit but it seems to have 100% hit to me, LOL. Never seen it miss.

Super Fang then cut your HP in half.

Hyper Fang or Crunch followed in 3rd round to finish you off as your hit yourself with Hyponisis again.

What's yours?

bloody zubat's supersonic is the same grrr. haha but the crocodile is waaaay to quick and waaaay to powerful for my liking

Any Pokemon with the Sturdy ability!

yeah this.. that is getting on my nerves -.-

Frigging Tranquill and Unfenzant using constant Detect, makes me waste valuable PP, especially since the AI pokemon always seem to get 2 to 3 Detects on a row.

Sturdy doesn't phaze me a lot, given that most Sturdy related pokemon are either Rock or Ground, and Scald's 20% to cause Burn can take care of it.

Are there any not annoying pokemons except Pikachu?   

Boldore mostly because of Sturdy.

Also, Watchog is pretty annoying with Hypnosis/Super Fang.  And Tranquill with the Detect combo.

But I got really annoyed with double wild battles with two Herdier and both having Intimidiate.

EDIT: Also, Foongus or Amoongus with Effect Spore.  Foongus ALWAYS seems to put my guys to sleep where as Amoongus usually paralyzes, if not poisons.

I thought Detect couldn't be used more than once consecutively, or is that Protect?

They are more likely to fail when used consecutively.

The chance decreases after the first use.  its 50/50 after the first and 25 for and 75 against after the second successful one.