If someone mentions to you that they were teased as a child, don't assume you know why and confidently tell them that you would never tease somone about obvious defect one or obvious defect two. I was on the receiving end of this one recently. I was thinking about obvious defect three, but the person's enthusiastic acknowledgements of the obviousness of the two previous defects sucked.
And the time, I let it go and didn't even mention the real cause of said teasing. But it has bothered me ever since.
When things bother me, I write about them.