When does teasing become harassment?

I have a Psychology seminar teacher that is really picking on me. I think she is bullying me and no one else in the class is brave enough to stand up against her on my behalf, so they all sort of laugh or just stay silent when she teases and picks on me. I don’t know what I ever did to her, but I swear if I give the exact same answer as any other student in the class, mine will get ripped apart while anyone else’s will get reasonable consideration. She has criticized my outfits, such as when I came to class in a sweat suit and she pondered out loud to the class whether or not we might want to agree on some minimum standards of dress, and so when I tried to dress really respectfully the next class she kept calling me Barbra Bush and making jokes about my membership in the young republicans club. She jokes as if we are all having fun together as a class, but I am not and she doesn’t direct her jokes at anyone but me. It is hard to put into words exactly what she does, and I think she is smart enough to know what lines she can and cannot cross – so there is very little that I think I can do to make a formal protest against her. I have spoken with other students in my class and they agree that she is very unfair to me. I have tried speaking to her about the way she treats me but she just blew me off as if what I was saying was totally ridiculous, and I think that speaking to her actually made things worse. What can I do to get her to back off? I have her for the rest of the year and I need this course? Thankfully the exam was multiple choice, or I am sure she would have taken me down on marks as well.