Rule #1 if you brought you car to the bar makes sure you have a ride home.
It's an old one. Bartenders and bar owners can even be held liable for someone crashing their vehicle after leaving your establishment.
I knew that they were responsible for the drunks if they crash, but I didn't know about the parking lot.
Alas, drunks don't usually show much common sense so they would tend to forget about Rule #1.