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

killer poke
 n.

    A recipe for inducing hardware damage on a machine via insertion of invalid
    values (see poke) into a memory-mapped control register; used esp. of
    various fairly well-known tricks on bitty boxes without hardware memory
    management (such as the IBM PC and Commodore PET) that can overload and
    trash analog electronics in the monitor. See also HCF.


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

killer poke

   A recipe for inducing hardware damage on a machine via
   insertion of invalid values (see poke) into a
   memory-mapped control register; used especially of various
   fairly well-known tricks on bitty boxes without hardware
   memory management (such as the IBM PC and Commodore PET)
   that can overload analog electronics in the monitor.

   See also HCF.

   (1994-11-04)