Every psychiatrist knows the DSM criteria for major depression: low mood, decreased self-attitude, changes in sleep, appetite, concentration, memory or sex drive, excessive or inappropriate guilt (and how do you judge that in a correctional facility?), anhedonia and suicidal ideation.
I would like to propose one small additional criteria:
Humor latency. Yes, a delayed or absent response to humor. Particularly my humor. Some people would claim that loss of humor falls under the anhedonia category, but I disagree. Anhedonia could mean almost anything: inability to enjoy knitting, exercise (but then almost everyone would meet criteria), coffee (never!) or Japanese existentialist literature. Humor is universal. Granted, some research suggests there may be gender differences in humor. Other research done on twins suggest that environmental factors play a role. (Where can I get in on a research gig that involves showing Far Side cartoons to twins?)
I'll grant the fact that men and women may appreciate different forms of humor. A male colleague of mine used to be prone to practical jokes---of the 'hide the rubber cockroach in the patient charts' kind of humor---and he referred to April Fool's Day as "Amateur Day". He had a problem with my puns. Or rather, he suffered from "humor latency". This is how he explained it: "I used to think I was just too stupid and didn't get your humor. But then I realized I did."
Now I know he was just meeting criteria.