A vampire who has been caught in a lie. Since vampires are undead and have no heartbeat, they are under no obligation to "cross their heart, and hope to die", thereby making them better liars than humans. However, having their lies discovered has the same consequences as a human lie.

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.