Hi Victoria,
For example, you could have said, Johnny, you need to enter this class with an open mind. You need to form your own opinion of me. This class is what YOU make of it. I am here for you. Try to end on a positive note. Make sure to request an appointment with Johnny. He needs to be spoken to privately about this. It is unfair for him to say things that can be damaging to your reputation in front of others.
Patricia