XD I think Larxene says it in a rude way though.
Larxene: She's says how you've gotten better but you still have a long way to go.
Maybe it's just me, but that sounded like a
compliment. I think my brain went dead for a second reading that. Larxene isn't polite by all means, so it probably was rude. Or came out rude. But, technically, if she was really mean, she would have said, "You still suck. Too bad for you, teehee :3". Or something along those lines. Yet, no. It was more that he's gotten better, but still putting him down rather kindly by saying he still has to improve only.
Then she gives a potion. I understand her line, but I expected some sucky item, or rather, nothing at all. Just...to go away.
And she didn't bitch in the second mission! Then again, did she even speak? >.>
...
Maybe if she wasn't bored all the time, and someone provides her entertainment, she'll be less uptight...
Or perhaps she just hates Sora, and likes Roxas better xD. And Naminé (before the bitchslap). I've noticed she's much worse to Repliku and Sora, while the blonds are more minor insults or taunting.