What does it mean when a guy gives you a mean look, but when you look at him, he looks away quickly and back at you?

Sometimes this guy looks at me through the corner of his eyes, so I don't think he likes me. I was walking in the hallway and when he saw me, he went behind this tall guy, but I could still see him looking at me through the corner of his eyes.
What does it mean when a guy gives you a mean look, but when you look at him, he looks away quickly and back at you?
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