dr.zli: elminster in BG1, extremely annoying, popping in only to utter some nonsense and disappear followed by my arrows and spells, sarevok is nothing compared to him!
Krypsyn: Elminster is just trolling the PC, he isn't really a 'villain' per se. But, yeah, he does do a mighty fine job of it! :)
However, using your reasoning, I'll have to change my answer:
The children of little Lamplight in Fallout 3. They troll, insult, and waste the PC's time, but can't even be killed with console commands. Maybe there is a mod for it allowing children to be killed in FO3 now. That would almost make me want to re-install the game.
I hate it how they made him invincible and used him as a troll. Through the whole forgotten realms lore they try to portray him as some wise and powerfull and invincible magician, yet he is a fool that needs to be removed.
About lamplight - you are absolutely right, there had to be "spank him/her" option in the dialogue and they did a poor job making children unkillable, If the player wanted to do it, he should do it and face the consequences of his actions.