Hmm... Who do I hate?
Heimskr is pretty annoying, my Dunmer killed him so he could have some quiet, my other characters tolerate him.
Others would be that racist dude harassing Dunmer, the Blackbriars and Silverbloods, Nazeem, that beggar in Markarth who wants me to steal from the temple, and likely some more I'm forgetting.
Edit: Any Thalmor who attacks me when I say I revere Talos as a Divine (I always do that to goad them into hitting first, it's like I'm giving them a chance to learn some tolerance for once and live. They don't learn very well though.)
These two are not really the character's faults as much but Bethesda's in limiting options.
I got pissed at Eorlund Greymane for a while when he told me he could make me any type of Skyforge weapon I wanted, and neglected to mention he doesn't have the only type I use, warhammers.
I also had issues with Skjor and despise Farkas.
Skjor.... infecting me with the dog disease and his attitude. I was seriously surprised to learn during my chat with Kodlak that my motivation for the last few of their missions had been to "avenge the death of Skjor" - my motivation had in fact been to blast through their questline as quickly as I could to get rid of the dog disease again.
I didn't hate Skjor, but was pretty miffed when O realized I couldn't continue the Companions without joining the Circle. And I also rushed through the questline quickly to get cured, not really for Skjor's sake but because I wanted to be in a Fighters Guild without having to be a werewolf.