Discription of Events: Was driving very slowly in the carpool lane surrounded by traffic leaving room for 5 cars to fit her and the next car in front of her in. When we tried to pass her she sped up and then slowed down to keep us back. We decided to go to the right of her to get out of there, while we passed her (slowly in traffic) she seemed enraged and was yelling at us. She then rolled down her window and threw a rock at our car. We took the closest exit possible to get away from her.