Write your own rules for how you treat people. Keeping them when nobody checks is what makes them yours.

A rule somebody else enforces is a condition of being in the room; a rule you set is a description of who you are. Writing them down turns vague intentions into something you can fail at, which is uncomfortable and necessary, since a value you never stated cannot be checked. Keeping them when nobody is watching is the whole mechanism by which they become yours.

Write three tonight, short and specific: no talking about people behind their backs, answer honestly when asked, never be the one who makes a new kid feel stupid. Keep them where you will see them. Break one, notice, and start again the same day.