If he rejected me, then why stare at me?

--For example i was walking to class and he was on the other side of sidewalk, it was kind of leveled up and he saw me, he was about to cross the tree, and he backed up, leaned back and stared at me with no expression for three seconds and went on walking to his class. i saw this all from the corner of my eye..
--- if we ever pass by each other he looks at me from the corner of his eye also...
-- so my question is why do guys stare at the girl they rejected?
If he rejected me, then why stare at me?
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