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

UBD
 /U?B?D/, n.

    [abbreviation for ?User Brain Damage?] An abbreviation used to close out
    trouble reports obviously due to utter cluelessness on the user's part.
    Compare pilot error, PEBKAC, ID10T; oppose PBD; see also 
    brain-damaged.


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

User Brain Damage
UBD

    (UBD) A description (usually abbreviated) used to
   close a trouble report obviously due to utter cluelessness on
   the user's part.  Compare pilot error; opposite: PBD; see
   also brain-damaged, PEBCAK.

   (1998-08-27)