1. I was secretly more popular in high school than I thought I was, so everyone knew me even if I didn't know them. And why wouldn't I be, with a face like this?
2. Similar to #1, but not so much popular as recognizable. As in, "Hey! I remember him--he was that white guy I went to school with."
3. A variation on #2: Perhaps one of the other two** white guys I graduated with was more popular than I and people are mistaking me for him.
4. The whole experience was just so traumatic that I've blocked it out.
5. I was so self-absorbed in high school that I failed to recognize there were other people around me***.
6. I am not really me, but rather a clone of me who was given (most of) my memories in order to pass as me while the real me rots in a secret prison somewhere in La Mancha.
7. Alien abduction****.
*And when I say "any of the people" I mean anyone but you, dear blog reader who happens to be a high school friend who has recently found me on Facebook. Because of course I remember you.
***Note that this is likely true (of me in high school as well as me in the present) whether or not it explains the failure to remember old acquaintances.
****Note that #6 and #7 are not mutually exclusive.