Biff's second wish was granted to the nearest person to him, which in this case was Sarah.
She moved in front of Biff to see what he was yelling about and saw his new vagina. It looked so weird being on the body of a guy. About as weird as seeing a penis on the body of a girl, anyway.
"I'm a freak. I'm a freak," Biff said. "Why the fuck is this happening to me?"
"You mean us," Tiffany corrected him.
Sarah backed away from them. What if they had some sort of a disease or something? It seemed unlikely, but what else could explain what happened to them? If she didn't get out of there, she could be next. She didn't want to have a cock between her legs, like Tiffany.
"Sarah?" Tiffany said, noticing that Sarah was heading towards the door. "Where are you going? We need to figure this thing out."
But Sarah didn't stop. She grabbed the door, pulled it open, and dashed out into the hallway like her life depended on it.