Jazz's behavior is over the top, and Zoey needed to check her. Ok, be mad, but don't be a total bitch to her in her own apartment! She spat gum in Zoey's drink and then sat back down on Zoey's couch like it was nothing. Go back to your dorm. It's amazing that Zoey is so intimidated by her given that Zoey was a "cool girl" in high school right? Once she saw Jazz was taking this to another level she should have disengaged.
However, this fits in with the whole big fish in small pond goes to college and becomes small fish in big pond theme for this show and especially this season.
Zoey's crisis of confidence was realistic even though it was framed in a very shallow and narcissistic package. I wish they had showed her struggling more with the design classes. Her epiphany about not loving design would have felt more earned. This seemed like she was quitting something she no longer enjoyed because it wasn't as easy or fun as she thought.
I miss the more ensemble feel of the show. The focus on Zoey is making her more unlikable and annoying.