I remember the first time that happened to me
In college, strangely along the same street I described above. Sunny day, nice weather, I'm just the typical grungy college kid walking to class. I turn a corner, and several meters ahead is a middle-aged woman walking in the same direction. After a moment, she notices me behind her and calmly, but swiftly, cuts across the street to the other side and keeps walking.
That had never happened before and it really broke my view of the world. Made me really sad.