Have to agree about the underwater monsters. You dive deep, kill one, and then you have to quickly resurface or you drown to death. This is especially annoying when you're in a sunken ship and when you have to find a hole to the top quickly without, hopefully, aggro a bunch of monsters/ghost/whatever along the way.
Though I still rank Murlocs ahead of them. Probably because, given that my main is a Warlock, she has the advantage of 'unending breath'. ^_^
Also have to agree about the quest monsters. You grind like 50-60 of them just to get ONE item. You can literally spend hours, clearing the area where they are, level up, and still not have it drop (while some lucky bastard could have gotten it on the first one or two kills).
However, even those quest, it isn't too much of a problem for me. Annoying and time consuming yes, but usually, they are easy kills.
Murlocs though, besides the annoying sound they make "RwlRwlRwlRwl", many times when you're trying to kill just one, you aggro one next to it. Very annoying when I'm playing my non-pet classes (Paladin, Warrior, Rogue, Priest), and then the bastard just has to run away aggroing more. :headbanger:
I know there are other monsters like that. But the Murlocs stand out more because they are one of the most common monsters you 'have' to kill for a given quest.