Why would someone stare at you when they think you don’t notice?

This has happened to me many times in class, lecture or at work with people who dislike me. I notice them staring at me (they sit a few rows in front of me) when I was reading, looking at my phone or turning around to put my jacket on and when I look back they turn away and later try to stare again. Why do they do this if they dislike me? If I would hate someone I would either avoid them completely or stare them down so that they notice.

Why would someone stare at you when they think you don’t notice?
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