[Saddlepoint]

I really feel like you guys don't get it. Allow me to explain.

The joke cleverly supplants the last name of poker pro Paul Darden for the term "partum" in "postpartum depression." Since, in the hypothetical scenario of the joke, Darden was the cause of the protagonist's misery, it follows that he (the protagonist) would suffer from "postDarden depression." Also, in order to understand the joke, you must understand that postpartum depression is a real condition that affects millions of women a year.

Those who are curious can read more about postpartum depression here.