Boy requests for the 3rd time on Instagram?

Hello, a boy has sent me a request on Instagram for the third time, although I have previously declined all two requests. I would actually just block him straight away, but now I am wondering whether I should do this instead of making it clear to him straight away why he keeps thinking to annoy me even though I keep my distance, because I know him from work. Even though I have told him at least once clearly that I don't want anything from him, it seems to have passed him by. I have never described anyone as weird, but that completely applies to him. He is not interested in my character at all; as soon as I said no, the next minute he asked me about 2-3 other colleagues. He wants a girlfriend, at 19. I am 22, and I find him immature because he is behaving really strangely. He still waits for me from time to time and stays in my showroom, waiting there, killing time until he catches his bus, even though I told him I didn't want anything from him when I took him aside one day. But on the other hand, I was still nice to him, especially because I felt sorry for him; all the girls were bad-mouthing him. Maybe he's taking something the wrong way, just doesn't understand despite my directness. He tries to flatter me by using pet names and just touching my hair. It seems very awkward. How should I react? I'm starting to honestly wonder what he's up to and I'm getting angry. Or should I just block him?