Roger Jackson posted these rules why you should smile:

1. It makes suspicious people wonder what you are up to.
2. It makes jealous people think you have something they don’t.
3. It makes envious people think you are up to something.
4. It makes your enemies think you have won.
5. It gives the impression you are happy.
6. It makes people want to follow you around smiling, too.
7. It means you have enough to spare so you are giving them away.
8. It recommends your religion.
9. It takes the tension out of bad situations.
10. God wants you to (and so do I).

I replied with a personal thought I jotted down in my notebook a few days ago:

Die with a smile on your lips. Since you don’t know the hour of your death, smile now.

And how about #11: It takes less effort and fewer muscles than frowning.