Now, don't get me wrong - it's not that I rejoice in this. However, a person has to CARE to not like you.
It's especially interesting when it involves someone you don't necessarily see regularly. Surely, it's easy to be bothered by the regular annoying qualities of a coworker or a classmate. However, to carry a dislike for someone who is no longer a part of your life seems to be reserved for those who've committed only a handful of serious offenses against you.
Although there were plenty of people from both high school and college who I didn't exactly like at the time being, I can honestly say I can't think of anyone I actively dislike from either place (and I am still looking for someone who will describe me as 'forgiving'). Anyone who wasn't to my liking is no longer in my life at this point, and the people who aren't in my life aren't worth the energy for the most point.
However, once in a while, we'll all come along a little nougat of info that someone we haven't seen/talked to/even thought of in forever REALLY DOESN'T LIKE US. There's some satisfaction in knowing that we must, on some level, albeit negatively, matter to that person.
As I'm sure you've inferred, this has happened to me recently. Of course, despite what I've mentioned above, this situation is of course clouded by the ever-persistent human question - "why?"