He stares at me when I'm not looking and smile?

Well, this guy usually stares at me when I'm not looking. I kind of feel his eyes on me. And he smiles. When he's far, he looks in my eyes and has a little smile but when we're close, he only glances and when our eyes meet, he quickly looks away.

We don't talk to each other and I barely know him. He's not the shy type, more a popular one.

Why does he do this?
He stares at me when I'm not looking and smile?
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