thinking of the `rm -rf` one, here is a fun take:

  export $WORKDIR=Home/me/proj
  ...
  rm -rf /$WORKDIR

If something unsets $WORKDIR or does not set it at all, wave bu-bye to your everything. And before you say "who would do that?!" -- I believe I heard that happened to a build of RedHat that also had some kind of force push and auto-pull and build on their version control so every connected person had their version of the software nuked. If not for the non-connected individuals, the entire software would be gone apparently. Or so the legend goes.