We had nothing in common in high school; I don't think we said more than five words collectively in the four years we were stuck in that building together. Sure, we're Facebook friends, just because it's cool to add everybody in your graduating class to your friends list when you first join, but that doesn't mean I want to talk to you in the real world.
These meetings always go the same: "ah crap, we both saw each other, now we have to say hi". The stammering conversation that grinds to a halt after you both ask how school's going. Then seeing them a half-dozen times after you say goodbye.