This just struck me as so "cute" that I had to share.

# Usage:
#
#   if find_bug then
#     bug! "unknown bug found"
#   end
#

class ScriptBug < Exception; end

def bug!( message = 'must not happen' )
  raise ScriptBug, "\n[SCRIPT BUG] " + message
end

Lovely, Minero Aoki! :)
T.