Diagram of ABO blood antigen system

“…Here, a person’s blood type is popularly believed to determine temperament and personality. “What’s your blood type?” is often a key question in everything from matchmaking to job applications.

According to popular belief in Japan, type As are sensitive perfectionists and good team players, but over-anxious. Type Os are curious and generous but stubborn. ABs are arty but mysterious and unpredictable, and type Bs are cheerful but eccentric, individualistic and selfish.

Four books describing the different blood groups characteristics became a huge publishing sensation, selling more than five million copies…” (BBC News via Boing Boing)