I do hate the quest NPCs that stalk you, but they don't compare to the person who is known to stalk me and several of my friends. They attach themselves at random to one of us and then proceed to follow us everywhere they can across Tamriel. Farming, questing, patrolling guild traders, doing public dungeons, crafting something... It doesn't matter what you're doing. If the area isn't group instanced, you will be followed. Not even our homes are safe, because this person will port to our homes and follow us inside of them... All without saying a word. I suspect this person just wants attention or friends, but they're doing a mighty fine job of getting exactly the opposite.
Personally, it got to the point where I remain marked offline when playing ESO unless I'm doing something that requires me to be visible. I've also banned this person from all of my houses.