Because since I came back from Portland, I run into someone I know from high school every week. Which, I guess would be ok if we had something to say to each other, or if I used to know them. But we don't and I didn't, or at least not very well.
I'm a jerk. I'm well aware. If I see someone that I know, but that I don't have anything to say to anymore, I just won't say anything. I assume that person wouldn't remember me anyway.
Perhaps this is misanthropic of me, but I really feel it's better than the awkward small talk that results from saying hello.