At work once there was a shared Excel spreadsheet which contained preallocated serial numbers to use (they didn't want to use sequential serial numbers but they had to be unique, so they were centrally allocated in blocks). I used to take the serial numbers I needed from the folder for a sister team which was in a directory *Z:\My Department\Sister Team\Serial Numbers (*my team's directory was Z:\My Department\My Team). This is where a colleague had told me to get the serial numbers from when I started. One day there was an empty new folder next to the Excel file with path Z:\My Department\Sister Team\Serial Numbers\FUCK OFF {my team} YOU HAVE YOUR OWN SERIAL SPREADSHEET\. Who knew NTFS had a built in messaging service?