Why does a guy stare at me when I’m near him?

There’s this guy that started at me when I’m close to him and watches me do my work but when I look at him he looks away. I can see him from the corner of my eye just staring at me without looking away wherever I’m standing aswell

why do guys act sneaky with their stares and act like we don’t notice them?
Why does a guy stare at me when I’m near him?
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