Not really hated, because they are somewhat necessery... but always confusing:
Health Potions!
Argh! I've been stabbed a hundred times by enemy swords, clawed by monsters bitten by Zombies, Burned alive by Dragons breath... let me just take a sip of this potion and all my gaping and bleeding wounds will heal INSTANTLY (or over a VERY short amount of time)
That there are so many ill and crippled people in RPGs... WHY don't they just take a health potion? these worlds have literally NO NEED for a doctor profession, because you can buy these things infinitely in every shop in the world!
or take the 3D Mario Games (64, Sunshine, Galaxy) - he gets wounded by all kind of things... but as soon as he grabs a COIN he heals these wounds...
another thing RPG-related:
MONSTER dropping GOLD-COINS (or the RPGs currency) after they are defeated... how did these monster get the gold-coins, and where do they hide it?? (I'm not talking about humanoid enemies but the REAL Monsters, like dragons, or demon-dogs or whatever)
and the WoW-Quest syndrome:
I'm on a collecting quest... I have to slay monsters to get hold of their eyes (for whatever reason)... sooooo Why didn't the 4 eyed-Monster I just killed have ANY eyes???? I'm certain I didn't strike the head! WHY????