I dislike Lae'zel too, but not really any more than the others party characters. They are all pretty terrible. In fact, Lae'zel is one of the better ones. (I dislike Astarion the most).
From what I have read so far in this forum, Astarion has to be the most disliked companion. Personally, I have done 3 playthroughs, and I either killed him or left him to rot in my camp. I just can't stand the way he talks and his manners. He's too over the top evil to be interesting.
Lae'zel is a githyanki and thinks all other races are inferior to her, hence the way she behaves.
