This short dialogue is from the movie Nick and Norah's Infinite Playlist:
Nick: Do you guys talk a lot? Talk about her (Tris) new boyfriend?
Norah: I cannot believe Tris dated a straightedge. That's, like, astounding.
Nick: What did she say about me? She said I was a straightedge?
Norah: Can I ask, what did you see in her? I could floss with that girl.
Nick: This is your friend that we are talking about?
Norah: All right. I'm the bad guy now. Is this what we're doing? I'm the bad guy?
Background: Norah is into Nick, but Nick is hung up on his ex-girlfriend Tris. So here when Nick brings up Tris, Norah is apparently miffed.
Having checked Urban Dictionary, I haven't found a definition that fits the context. Urban Dictionary mentions "show off" but it doesn't seem relevant. From what Nick says after that line, it seems Norah's words are not very flattering. What does it mean here?