Prosopagnosia.

The inability to recognize faces.

People with face blindness can typically understand facially expressed emotions — they know whether a face is happy or sad, angry or puzzled. They can detect subtle facial cues, determine gender and even agree with everyone else about which faces are attractive and which are not. In other words, they see the face clearly, they just do not know whose face they are looking at, and cannot remember it once they stop looking.

How strange. A person with this problem must have many painful social encounters, especially before being diagnosed. On the other hand, many of us are just lazy about noticing and remembering people. We could make casual claims of prosopagnosia, the way we make casual claims of attention deficit disorder.