The Collaborative International Dictionary of English v.0.48:

Demented \De*ment"ed\, a. [From Dement.]
   Insane; mad; of unsound mind. -- De*ment"ed*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

demented
    adj 1: affected with madness or insanity; "a man who had gone
           mad" [syn: brainsick, crazy, demented, disturbed,
           mad, sick, unbalanced, unhinged]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "demented":
   abnormal, bereft of reason, brainsick, crackbrained, cracked,
   crazed, crazy, daft, delirious, deluded, deprived of reason,
   deranged, disoriented, distraught, flighty, frenzied, hallucinated,
   hysterical, insane, irrational, loco, lunatic, mad, maddened,
   maniac, manic, mazed, mental, mentally deficient, meshuggah,
   moon-struck, non compos, non compos mentis, not all there,
   not right, odd, of unsound mind, off, psycho, queer, reasonless,
   senseless, sick, stark-mad, stark-staring mad, strange, tetched,
   touched, unbalanced, unhinged, unsane, unsettled, unsound,
   wandering, witless



The Jargon File (version 4.4.7, 29 Dec 2003):

demented
 adj.

    Yet another term of disgust used to describe a malfunctioning 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. Compare wonky, brain-damaged, bozotic.


The Free On-line Dictionary of Computing (30 December 2018):

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)