Jon Ronson's "Psychopath Test"
In this decidedly spooky TED Talk, Jon Ronson explains his journey to understand mental illness, which brought him to a prison for the criminally insane to interview a very sanely-dressed possible psychopath, then brought him to "Chainsaw Al" Dunlap, whose house was "like Narnia." The whole thing is engaging, challenging, and makes me really want to take the test.
Bonus points if you get the reference on Ronson's tee shirt without Googling it.
This is all discussed in more depth in Ronson's book The Psychopath Test. Also very relevant: This American Life: The Psychopath Test. You can take a kind of psychopath test online, but I'm assuming it's not the same form that Ronson refers to.