Politeness comes in many forms, but one way in which it manifests itself regularly in the workplace is holding the door open for someone. Studies have shown that if we leave it to individuals to open doors for themselves, society will quickly decline into chaos and anarchy. This is why more advanced societies, such as those found in hotel lobbies and Gold Class cinemas, employ people whose sole occupation is to open doors. We should study these societies more, as they will lead us all to enlightenment.
It is important, then, to maintain the delicate balance of our society by ensuring that you open as many doors as are opened for you. This can be easy when there are two doors within quick succession, but otherwise it is highly recommended that you keep score. Keep a note of how many times the door has been opened for you, and how many times you have opened the door for others.
Also keep a note of the people who never seem to hold the door open for anyone. These are the types of people who are likely to use your coffee mug when you are not in the office, or borrow your scissors to cut their nails.
People who big-note themselves by always holding the door open, and who make a point of ensuring that everyone can see they are doing that, should also be noted. These are the types of people who are likely to use your coffee mug when you are in the office, or borrow your office scissors to cut their pets' nails.