You're out walking in downtown Spokane.
You see someone coming who looks familiar. You can't place him. But you are pretty sure you have crossed paths with this person at one time or another.
So you say "Hello."
And Mystery Man just walks on by without saying anything.
What to conclude?
A) He has a hearing impairment. B) He was lost in deep thought. C) You don't really know him and so he didn't realize the greeting was intended for him. D) You do know him but can't recall the context because you dismissed him as a jerk long ago. E) He does not like you either. F) Whatever the circumstances, he's not worth two more seconds of consideration.
I went with F.