from
The Free On-line Dictionary of Computing (8 July 2008)
like nailing jelly to a tree
nailing jelly
<jargon, humour> Used to describe a task thought to be
impossible, especially one in which the difficulty arises from
poor specification or inherent slipperiness in the problem
domain. "Trying to display the "prettiest" arrangement of
nodes and arcs that diagrams a given graph is like nailing
jelly to a tree, because nobody's sure what "prettiest" means
algorithmically."
[{Jargon File}]
(1997-12-23)