Most Annoying Creatures

[Team Flare Zakk ( Agatio )]

In Golden Sun The Broken Seal

I don't know, maybe enemies that appear early game when you are low leveled and without Mia.

[Star Magician]

If you go to Mercury Lighthouse before Kolima, the tundra monsters can be kind of annoying since they are higher leveled than you are, but that makes it more challenging and a bit more fun :P

Oh, and this kinda goes without saying, but random encounters in the overworld are annoying no matter what game you're playing >.>

[Tetsu (Soltur)]

Or the Tornado Lizards. Or Tempest Lizard.

[Douglas]

I personally never had an enemy I considered to be annoying... well, actually, no.  Maybe Stone Soldiers.  Never worth the pitiful XP rewards, considering their habit of using Dynamite.

Agreed.  When they use Dynamite (self destruct), not only do they inflict considerable damage, but you also receive no exp. 

[Tetsu (Soltur)]

Stupid suicidal maniacs. *Soltur casts Stabby-Stab! Stone Soldier 1 takes 9000 damage!!!*