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

neat hack
 n.

    [very common]

    1. A clever technique.

    2. A brilliant practical joke, where neatness is correlated with
    cleverness, harmlessness, and surprise value. Example: the Caltech Rose
    Bowl card display switch (see Appendix A for discussion). See also hack.


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

neat hack

   1. A clever technique.

   2. A brilliant practical joke, where neatness is correlated
   with cleverness, harmlessness, and surprise value.  Example:
   the Caltech Rose Bowl card display switch.  See also hack.

   [Jargon File]