My fav as an Imperial - Do a quest for a Nord....they thank you....you come back and see them later and get "I hate Imperials!" or something to that extent. The old lady in the alchemy shop in Riften is one example of this.
Yes some questgivers swear "cat" after I have helped them. Yes it is an smart thing to say to someone who just cleared out an fort than they are alone.
Most surprised that they have an grand soul


