Mask off is a term derived from 'The Mask of Sanity: An Attempt to Clarify Some Issues About the So-Called Psychopathic Personality', a book written by American psychiatrist Hervey M. Cleckley.

A psychopath, by clinical definition, is someone born without the ability to experience genuine human emotions. In order to receive acceptance from society, the psychopath, from a very young age learns to expertly mimic the emotions of a normally functioning person. This is referred to as the ability to 'mask' or disguise the fundamental lack of internal personality structure.

'Mask off' refers to the periods of time where the psychopath drops this false façade, which normally results in repeatedly purposeful destructive behavior, often more self-destructive than destructive to others.