All of the talk about classroom rules reminds me of the song I used to sing to my students if they said something rude in class. Believe me when I say that my singing is awful, and they didn't really enjoy hearing the song. I'm not sure who wrote the lyrics, but it seems like a grasshopper sang it on one of my records I had as a child. I always told my students it was the grasshopper song.
If You Can’t Say Something Nice
If you can’t say something nice,
Shh, say nothing...
Take a piece of good advice,
Shh, say nothing...
Think of something nice to say,
That’s the path to follow,
If you can’t say something nice,
Close your lips and swallow!
The song might make a great poster and be a little more meaningful than a list of rules.