If you shouldn't drive after having a drink or two, you definatly shouldn't carry a firearm after drinking. Most of the time, when stopped for suspicion of DUI, you can breath test under the limit and still be arrested. It all depends on the opinion of the officer on scene, and if you are too impaired in their opinion they will arrest you. I imagine the same applies for a self defense shooting...
Carrying a firearm when everyone in your group wants to have a few drinks with dinner, while it does suck to watch them have tasty brews and keep yourself with Diet Pepsi, does eliminate the need to fight over who will be the Designated Driver.
