It is Not Considered Polite...

...to stick your fingers in your ears when someone is singing.

In Conversations...

Do not interrupt the person who is talking to tell them they have something in their teeth.  This is considered rude. Wait until they finish their sentence first, then talk. 

Before You Leave the Bathroom...

Check your shoes for the random piece of toilet paper, and make sure that your skirt is pulled down instead of stuck in your underpants.