Did you ever come across any kind of creature or race in any work of fiction that somehow just triggered your bad side?
For me, it's the orkz from warhammer 40k. They just seemed like such a random thing that has no place in the grim dark setting of warhammer. "They can build anything they set their mind to" What the hell kind of crap is that?
Please explain what made you hate them; is it the way they acted, things they did or said, or their appearance?