Most annoying monster in the game...

[Tessai]

Ifrit and vendors who sell useless crap.

Nuff said.

[yhjuiioklko]

=o, I think all the MVPs are pretty annoying... all that summoning slave trash and disables 

[Ganondorf]

Ancient Mimic: This mob is annoying when it's hopping around everywhere and even more annoying when you hit it.  AHAEHAEHAEHAEHAEHAEHAE.  Ugh.

Muka: The sound is just awful.

Gazeti: The hit lock is super irritating, especially if you're a poor Wizard/High Wizard without a Phen Card or anything trying to train there.

[scrollLock]

I also hate these, f*** useless piece of s*** in ragnarok, totally useless.

[Leamee]

I have a list of 'em:
Mimic, Ancient mimic, Gryphon T_____T
Seeker, Salamander, Bow Guardian/Master
Any MVP/mini boss that creeps up on you and OHKOes you when you're still low-level > stormy knight in Toy 2 in particular
Bombs in Kiel > killable but makes you play russian roulette with your exp.

[Neiru]

Chon Chon. The attacking one.
I remember jobchanging on the official RO servers, and this Chon Chon is irritating and blocks my mighty way of jobchanging -_-"