Your brother!!

You look at her, and say, "Ummmmm, neither Nicole, you will not believe me but I am actually your brother!!" She looks at you for a second taking in your new body and starts to laugh, "Good one, no seriously who are you?"

You rack your brain trying to come up with some way to show her that you are actually her brother. As she was laughing you said, "You remember when we were young and we got caught breaking into the neighbor's house and I let you get away you would not be punished and stopped from going out with your boyfriend?" That did it, she instantly stopped laughing and looked at you with an expression of surprise.

"Okay," she says looking at you with a nonbelieving face, "is that really you John? How is that even possible?"

You sigh, "Nicole it really is me, I promise you. I went out partying last night, I blacked out, and then all of a sudden when I woke up I was a girl. I could not make this kind of story up if I tried. Please you have to believe me."