Why do these guys in my class throw things at me?

Sometimes, when I'm just minding my own business doing my work or taking notes or doodling, they'll throw paper balls at me. I ignore them, but they still continue to do it. They don't do this to any of the other girls in class, and so I can't help but feel a little hurt and self conscious whenever they do this. Do they do this because they think it's funny? How can I get them to stop?
Why do these guys in my class throw things at me?
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