Being bullied? Is this ual harment?

Well im 15 years old and im a girl and theres a guy on my bus who every once in a while really pisses me off. I dont even know him! Im rather quiet on the bus as i dont know anyone, so i dont see what he has against me as i barely ever see him and nevermind talk to this ! The first incident happened when i was waiting for the bus after school. I was standing alone listening to my ipod when he came up to me and put his arm around me! I quickly walked far away but he followed me and did it again! I was disgusted. The second time i was sitting on the bus playing my ds when he told me to get up and move so he could sit there. I ignored him and kept playing my ds. He had the nerve to press the ons on my ds and then called me "a witch" and "cinderella" wtf? So today i got on the bus and listened to my ipod and he said "hey shawty" and sat behind me and began petting my hair and rubbing my shoulder. I gave him a nasty glare; he stopped and all his friends started hollering saying "oooo she gave you a dirty look!" idk what to do anymore. Ive never seen this pervert at school, just on the school bus. I dont even know his name! I keep to myself just like everybody else, so why am i a target??? Should i cuss him out or just remain silent? Thank you so much