"You're Type A, Aren't You?"

...a teacher asked me not too long ago.
"Type A?" I immediately thought she meant Type A personality. (Which, it turns out, she did, except in the Japanese way)
After some chattering with her coworkers about how to translate what they wanted to say to English, she said, "Blood. Blood type."
"Type A blood?" I asked.
"Yes."
"Yea, I have Type A blood. Why do you ask?"
"We thought so."
"You thought so?" My mind started searching for an explanation, and I came up with no reasonable explanation for how they predicted - or even why they cared about - my blood type.

But turns out that one's blood type here is a personality guide. It's the equivalent of astrology in Japan. If you're type A, you're considered to be a perfectionist. Type B, selfish. Type O, you're supposedly someone who focuses on style over substance. Type AB's are said to have a split personality between the A and B types, but also having a need to always be free.

A few days later, in a different teachers' class, the question was asked of me again. This time the teachers' debated whether I was Type A or B before they asked. Later, I was erasing the whiteboard and missed a couple lines over to the side of the board, so I went to erase them too. As I did, someone said, "See? He is Type A."

Wikipedia has an article which goes into greater detail.

If it is like astrology in the States, I humorously picture a man trying to pick up a woman at a bar with a line like, "You're Type A, aren't you? I can tell..."