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

Wrong Thing
 n.

    A design, action, or decision that is clearly incorrect or inappropriate.
    Often capitalized; always emphasized in speech as if capitalized. The
    opposite of the Right Thing; more generally, anything that is not the
    Right Thing. In cases where ?the good is the enemy of the best?, the merely
    good ? although good ? is nevertheless the Wrong Thing. ?In C, the default
    is for module-level declarations to be visible everywhere, rather than just
    within the module. This is clearly the Wrong Thing.?


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

Wrong Thing

    A design, action, or decision that is clearly
   incorrect or inappropriate.  Often capitalised; always
   emphasised in speech as if capitalised.  The opposite of the
   Right Thing; more generally, anything that is not the Right
   Thing.  In cases where "the good is the enemy of the best",
   the merely good - although good - is nevertheless the Wrong
   Thing. "In C, the default is for module-level declarations to
   be visible everywhere, rather than just within the module.
   This is clearly the Wrong Thing."

   [Jargon File]