Why are guys nice then mean and hostile for no identifiable reason?

This happens a lot. I'll get acquainted with a guy and it will be fine then the next time they will be downright hostile or pretend I don't exist.

Or do passive-aggressive and ungentlemanly things to me for no reason at all.

A lot of times, guys will look and spy from afar but will not be able to interact normally.

Really, I'm a chill person and I would be a beach bum if I didn't have things to do. I don't get it.

Why are guys nice then mean and hostile for no identifiable reason?
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