[Drugein]

Well, it's definitely true to some extent, since there will 100% be some genes that contribute in some way to a person's personality that are colocated with genes responsible for blood type.

[booleandilemma]

It's pseudoscience, nothing more.

https://en.wikipedia.org/wiki/Blood_type_personality_theory

[throwaway667555]

"nothing more" is an incorrect statement. The science is inconclusive, as science most often is.