A race of pointy-eared ancient humanoids, the most famous of whom is Spock, from a planet of the same name in the Star Trek series. The word could also be used by James T. Kirk to express shock or disbelief in any of Spock's logical thoughts or behaviors that were not clearly comprehended by the Captain.
Kirk: "Doctor, go ask that green slimeball thing if it's possible a human being could have sex with its species."
Doctor: "Damnit, Jim, I'm a doctor, not a sex therapist!"
Spock: "I am afraid the Doctor is right, Jim. That would be completely illogical."
Kirk: "Spock, you're questioning my orders?! Are you out of your Vulcan (fuckin') mind?!"