For the record, I have heard that schizophrenics also lack a sense of humor, and lack any appreciation of irony or other kinds of abstraction; they tend to interpret everything literally. That's why a simple test of sanity is to ask the person to explain a well-known proverb, like "Don't cry over spilled milk." An explanation by a schizophrenic would probably be specifically about milk.

Of course all kinds of mental problems come in varying degrees.