Why is he upset?

I didn't get into an argument with this guy, but I don't like him, and he's upset with me mainly because I rejected him. When I confronted him about his passive-aggressive behavior, I said, "The only reason you're mad at me is that I rejected you." He then claimed that I was trying to provoke him and that I have serious issues. However, he insists that his anger isn't related to the rejection. I'm struggling to understand why he is upset with me..

Why is he upset?
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