Why do guys throw paper down girl's shirts?

This Monday, I was in my Science class taking notes for an upcoming test when the guy who sits across from me starts throwing paper. At first I thought he was trying to peg the kid next to me in the face because he was being annoying, but after the third try he got a crumpled up gum wrapper in my camisole (just so you know I was wearing a plaid shirt over my camisole). I was mortified and my entire table was laughing. I laughed it off with them so I wouldn't seem so embarrassed but I was humiliated.

After that spiel, why do guys do that? Throw paper down girl's shirts, I mean.
Why do guys throw paper down girl's shirts?
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