I met a fellow today whom I haven't thought about for years. We were reintroduced, and I really put him down. He was not devastated, but I clearly got to him. At the time, I was fascinated that I had invented a nasty remark, and sorry that I had used it. He's a nice guy, and he didn't begin to deserve it.
I had walked into the lab to find a manager bringing a developer up to speed, a person I did not recognize. I started to introduce myself, but he said, “Toby, I remember you. We worked together ten years ago on the motion video project.” And he told me his name.
I remembered him at once. In fact, we had been acquaintances at best. We worked with the same people, but not quite on the same project, and our paths had indeed crossed quite often in 1999 and 2000. My response to him was, “I remember! You never answered my last email to you, in 2003.”
That was the putdown. And as best as I can recall, it's true. In 2003, I was looking for consulting work, and I had systematically emailed developers I knew of including, this Mr. X.
I wish I had saved my remark for someone who really deserved it. I can think of a lot of situations in which my remark would be even more devastating if I, and the other person, both knew it was false.