Scary: Chaurus Hunters. I'm fine when it comes to normal Chaurus's, cause as soon as I see one i shoot the living daylights outta it; But those Chaurus Hunters scare the shit outta me! when I first encountered one, i spilled coffee all over my controller :P
Repulsive: Hagravens and forsworn. With all their disgusting animal rituals with bloody animal parts all over their rooms... ewww. Theres nothing i hate more than seeing a quest that takes place in a forsworn hideout like Karthspire for example.
All the kids inhabiting Skyrim since they all act like dipshits. Specially Balgruf's kids, anytime that one kid would utter licking boots or w/e phrase at me I just go apeshit and slaughter him (got killable children mod)... then I reload and hope for the best. Remember kids, don't talk smack to the dragonborn unless you want to die D:
That's awesome Ben, you've probably unlocked Pandora's Box as far as killing annoying essential NPC is concerned.