One Japanese superstition says that blood-types are linked to personality:

A: calm, composed, serious, reliable, perfectionist, arrogant, emotions suppressed
B: curious, bright, cheerful, enthusiastic, uncoventional, superficial, unreliable, selfish
O: carefree, generous, independant, outgoing, social, flexible, clumsy, flighty
AB: sensitive, considerate, careful, efficient, strict, moody, unpredictable