Girls, how to not be awkward around a guy you rejected?

I seriously don't know how to act every time we bump into each other. I just friggin want to evaporate and magically disappear at times we meet each other. It's almost 4 years but i still feel awkward whenever i see him. I want to hate myself for remembering the tiniest details of the past (high school). I'm supposed to be over it at this point. I didn't actually told him personally but I kept avoiding him since the day I've known that he likes me (high school). I feel extremely pathetic not being able to gather myself up and not feel awkward.
P.S. Help me out girls. Pretty please! :)
Girls, how to not be awkward around a guy you rejected?
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