Since Mark started one about seat belts, I have to chime in with mine on drinking.
Working as a bartender I see how many people drink and drive everyday. Even all of my co-workers get into their cars after having a few, or more than a few. From personal experience about 90% of the people who go out don't call a cab or have a designated driver. It's disgusting. We live in Chicago, there are cabs everywhere. Even worse, my co-workers get completely blasted and drive home and can't even recall how they got into their home. It's a serious matter that the majority doesn't take seriously.
This link is really gory and is not suitable for the kiddos or the squeamish...
http://www.eatnineghost.com/do-not-drink-and-drive/