There is a pervert that sits next to me. What can I do?

Okay so I have this teacher for homeroom and photography but there is this boy who sits next to me and I get this scary feeling that he might want to touch me. Sometimes he text messages in homeroom and looks at himself on the computer screen. He would move alot and usually when we sit he would try to get close to me. There are times when we sit in class he would scoot his chair a little on my side and I tried to sit a little far from him. He looks lie a guy who would hang out with those gangster types. Sometimes when I get out of 5th period because I have a minimum day and he would sometimes ditch and ride his bike close to me or goes in the way where I go home. I see him in the mornings too but he would always ride his bike. Sometimes he rides it close to me. One time when I was walking to school this girl behind me was there and that pervert came and when he stopped at my way he slowed down. He was asking this girl Im not sure if there friends but he asked her to ride with him. I got so scared I dont know what to do. I want to tell the photo teacher if I can switch seats but she can be a meanie and picks on people alot. How can I convince her to switch me