Did you know that Koreans associate personalities with blood types? Depending on your blood type (A, B, O, and AB) you might be perceived by some Koreans as having a certain personality.
Type B Blood: Creative and passionate, but irresponsible, selfish, and lazy.
Type O Blood: Confident and expressive, but egotistical and risk takers.
Type AB Blood: Rational and calm, but critical of others and indecisive. Possibly a genius or a psychopath.
For a disclaimer, I don't believe that blood types influence people's personalities, but it is useful to know these when in Korea. It's also fun to ask a Korean to guess your blood type, and see if they can correctly do it or not.