Cicero, I can't stand him.
I also despise the children too...
A tie between Ulfric Stormfront and Cicero for me.
Never understood why people hate Cicero.. if people read his background through his journals, you'll understand why he's the way he is.
Spoiler I have lately felt guilty about killing him and have decided to spare him so I can take him as a follower eventually
If I had my way with her, I would marry her.. unfortunately not even the console seems to work in programming her

I suppose I could take Sapphire..
I can't argue with that..
Spoiler first time they asked me to kill Paarthurnax, I feel betrayed and disheartened.. I enjoyed the Blades in Oblivion but after Skyrim I wouldn't care if they were all gone
Also, as I've said in other threads like this.. no one NPC has annoyed me enough to want to outright kill them as I tend to just ignore all the ones I don't need to talk to. True, the same dialogue pops up time and time again, but I usually don't spend a lot of time in shops or out where the NPCs are. I also have a mod that reduces NPC pvssyr to the point where you have to bump into them for them to talk, but only because of how often I have to run through the cities.. I didn't want to hear the same dialogue every time I passed through to do something. I don't mind conversations between NPCs much though.