What etiquette rule do you wish more people were aware of?

Mine is that middle seat on an airplane gets the armrest

Edit: top 10 I liked from the thread:

1. Don't stand in front of me when we're in a circle of friends

2. Use your turn signal when driving

3. Don't incessantly post that you're single

4. Don't applaud at a concert performance until AFTER the conductor puts both his arms down.

5. Give up seats on public transportation to young children, older people, pregnant women.

6. When you want to get on a bus, train, etc, wait until everyone gets off first. Don't push your way through the crowd of people trying to get off.

7. Take off shoes in houses where the owners don't wear shoes, especially if it's clean

8. Don't own a dog if you can't be bothered cleaning up it's mess.

9. If you're walking out of a public place, hold the door for the next person right behind you

10. Don't use speaker phone while in a public bathroom... and observe other social rules in the bathroom