Psychology is a poor science. It's predictions hold little more credence than stereotypes. This is especially true in the idioms that trickle down to the lay person.

Could something as innocent as "half empty/half full" label one's whole character as pessimistic or optimistic respectively?

That's absurd.

Fuck the glass.

Besides which, most questions have objective answers; subjectivity is an illusion of ignorance, or perhaps custom.

As it should happen, I take great pleasure in providing definitive answers to such questions. So how does that qualify me?

Asshole, I expect.

How would you classify yourself?