@BG1 I thought that was the point of getting Xar and Montaron, cannon fodder
I haven't really played BG1 that much, but I waited until a number of guards were concentrated in front of the Inn, then had Montaron lure him within range of the guards, then have the rest of my party gang up on him. The trick is to kill him fast
Favourite hate/bad designs:
BG2TOB: Peasants and beggars with +3 swords and enough gold to buy a small mansion.
KOTOR: Beating the crap out of Malak to the point where he is wallowing around on the floor, trying to stuff his enthrails back in with his amputated hands, just to have that silly girl run to him, lock the doors and then surrender without a fight.
NWN2: Forced companions, "Grind" areas.
OBLIVION: Everything (maybe not quite fair, I only played it for 8 days)
EUROPA UNIVERSALIS III: Cheating AI
ALL: Quests that gets stuck in your "to-do" list when they have become unsolvable.
Probably a lot more, but those are the ones that is foremost in my mind.