The narrator of this song --
Is she singing about her ex, or about a boy she likes who only likes her as a friend?
Is she a stalker, or just a lovelorn girl? Is she an unattractive or plain girl, watching her secret crush pick up a prettier girl on the dance floor?
Is she a ghost? (Why don't you see me? I just came to say goodbye)
At the beginning, she definitely sings "I'm not the girl you're taking home," but in one of the choruses toward the end it changes, quite clearly, to "I'm not the GUY you're taking home." And that interpretation also makes sense: a girl sneaking into a gay bar to watch a friend (on whom she has a crush) pick up a stranger.
Help me, DL.