I used to believe this a lot.... But after evaluating many personalities and blood types, I don't think blood types tell all that much as people think. But I do believe that blood type sets a fundamental base for one's way of thinking... but how you look at the person cannot all depend on blood type. I know an A-blood girl who's a total b!tch but another A-blood girl who is funny and nice as hell.
By the way I'm an O blood.