Only recently I found out that my blood type is "O Rh negative". I suspected that I could be "O" as both of my parents seem to recall being "O's" themselves. But I had no idea that I am also Rh negative. That makes me a universal donor and means that I can get blood only from other people who also are "O Rh negative".
I was very surprised (and scared) to find out that less than 1% Asians are "O Rh negative" (e.g. only 0.03% of Thai population has this blood type, <0.1% of South Koreans, <0.3% of Chinese people). In the internet I saw several calls from Red Cross in those countries calling for people with this particular blood type to donate their blood... I will seriously consider if I want to travel somewhere out there for extended period of time. It seems that it might be like playing with a fire...
However, even in San Francisco, I might be in a trouble during any major disaster, as "O Rh negative" blood type is given to all patients who urgently need blood transfusion and whose blood type is unknown. That means that blood banks might be running low on my blood type.
It also means that I should regularly donate my blood. I tried to start doing it 13 years ago. On my 18th birthday I showed up in a hospital and I wanted to donate my blood. I was turned away by a nurse, that also happened to be my neighbor, as I did not have national ID with me! (I had other documents with me confirming that I am 18, but they were not good enough for them). It was a bit traumatic experience to me. I wanted to do something good and instead I got yelled at... That discouraged me from donating blood regularly. But now I have a strong motivation to get over my trauma.