dancing frog

from Jargon File (4.4.4, 14 Aug 2003)

dancing frog
 n.

   [Vancouver area] A problem that occurs on a computer that will not
   reappear while anyone else is watching. From the classic Warner
   Brothers cartoon One Froggy Evening, featuring a dancing and singing
   Michigan J. Frog that just croaks when anyone else is around (now the
   WB network mascot).

from The Free On-line Dictionary of Computing (8 July 2008)

dancing frog

   <programming, humour> A {bug} or {glitch} that only occurs for
   a particular user; never when the user tries to show it to
   anyone else.

   The term is derived from a Warner Brothers cartoon in which a
   man discovers a frog which can sing and dance; he believes
   this will make his fortune but the frog never performs in
   front of anyone else.

   (2004-10-16)