Asuka always has an angry side. It's buried from time to time, but she carries a lot of resentment around with her and it doesn't take much to bring it back to the surface. She doesn't meet his gaze (more accurately, she doesn't look at him) when he responds. She wants to believe that, but it's hard to. Especially when she feels like she's a third wheel.

"It's not like you actually care about me," Asuka shoots back venomously, "I'm just someone you know, right? A familiar face that you like to have around to make yourself feel better."

To be fair, that's how she feels about him sometimes. Besides, this is more to draw reaction (and maybe make herself feel better via anger).