How do I deal with annoying people?

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Whenever I am going to my next class, I usually run into this guy. He's a plain idiot, and everyone makes fun of him. But for me, he keeps bossing me around and he won't leave me alone. Such as, I'm walking to my next class with my girlfriend and this guy just pops out of nowhere and says: "Haha, I'm stalking you." And then he continues on pushing me (literally) and it's getting annoying. I told him to @#!$ off but he wont and it's ticking me off. Any ideas? I don't want to wack him or he'll call the police or something on me. I'm stuck.