pathological

pathological adj.  1. [scientific computation] Used of a
   data set that is grossly atypical of normal expected input, esp.
   one that exposes a weakness or bug in whatever algorithm one is
   using.  An algorithm that can be broken by pathological inputs may
   still be useful if such inputs are very unlikely to occur in
   practice.  2. When used of test input, implies that it was
   purposefully engineered as a worst case.  The implication in both
   senses is that the data is spectacularly ill-conditioned or that
   someone had to explicitly set out to break the algorithm in order
   to come up with such a crazy example.  3. Also said of an unlikely
   collection of circumstances.  "If the network is down and comes up
   halfway through the execution of that command by root, the system
   may just crash."  "Yes, but that's a pathological case."  Often
   used to dismiss the case from discussion, with the implication that
   the consequences are acceptable, since they will happen so
   infrequently (if at all) that it doesn't seem worth going to the
   extra trouble to handle that case (see sense 1).