Source : Webster's Revised Unabridged Dictionary (1913)

Demented \De*ment"ed\, a. [From {Dement}.]
   Insane; mad; of unsound mind. -- {De*ment"ed*ness}, n.

Source : WordNet®

demented
     adj : affected with madness or insanity; "a man who had gone mad"
           [syn: {brainsick}, {crazy}, {distracted}, {disturbed},
           {mad}, {sick}, {unbalanced}, {unhinged}]

Source : Free On-Line Dictionary of Computing

demented
     
        Yet another term of disgust used to describe a program.  The
        connotation in this case is that the program works as
        designed, but the design is bad.  Said, for example, of a
        program that generates large numbers of meaningless error
        messages, implying that it is on the brink of imminent
        collapse.
     
        [{Jargon File}]
     
        (1994-12-07)