This one made me LOL:

   My mistake on SunOS (with OpenWindows) was to try and clean up all the
   '.*' directories in /tmp. Obviously "rm -rf /tmp/*" missed these, so I
   was very careful and made sure I was in /tmp and then executed
   "rm -rf ./.*".

   I will never do this again. If I am in any doubt as to how a wildcard
   will expand I will echo it first.

I read this, and just had to go try it because I couldn't picture it in my brain. Here it is:

   $ echo ./.*
   ./. ./..

So if you're in /tmp/ and do 'rm -rf ./.*', it's

  rm -rf ./. ./..

and ./.. is .. which from tmp is /. Thankfully we have protections against this now. Back then, not so much.