How do I tell this guy to leave me alone?

I ride the bus to get to college and normally keep to myself. Today I’ve seen on the bus before came up and started talking to me. He seemed okay at first, but then in the next five minutes of talking to me, he revealed that he’s younger than me (which would maybe be okay), that he skips school on a regular basis, that he’s been arrested, and that he does not know what the word “necessarily” means. He then asks if I’m single and if he could have my number.
While I’m flattered, I have absolutely no interest in this guy, and I see him fairly regularly on the bus. How do I tell him that I want him to leave me alone without upsetting him? I’ve already figured that I could just start reading on the bus, telling him explicitly that I don’t want to talk to him, etc. What thoughts do you guys have about this? I need help!