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

smash case
 vi.

    To lose or obliterate the uppercase/lowercase distinction in text input. ?
    MS-DOS will automatically smash case in the names of all the files you
    create.? Compare fold case.


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

case sensitivity
case insensitive
case sensitive
fold case
smash case

    Whether a text matching operation distinguishes
   upper-case (capital) letters from lower case (is "case
   sensitive") or not ("case insensitive").

   Case in file names should be preserved (for readability) but
   ignored when matching (so the user doesn't have to get it
   right).  MS-DOS does not preserve case in file names, Unix
   preserves case and matches are case sensitive.

   Any decent text editor will allow the user to specify
   whether or not text searches should be case sensitive.

   Case sensitivity is also relevant in programming (most
   programming languages distiguish between case in the names of
   identifiers), and addressing (Internet domain names are
   case insensitive but RFC 822 local mailbox names are case
   sensitive).

   Case insensitive operations are sometimes said to "fold case",
   from the idea of folding the character code table so that
   upper and lower case letters coincide.  The alternative "smash
   case" is more likely to be used by someone who considers this
   behaviour a misfeature or in cases where one case is
   actually permanently converted to the other.

   "MS-DOS will automatically smash case in the names of all
   the files you create".

   (1997-07-09)