I was at a corporate function this week and the beers were flowing. I was drinking coke zero. Nobody asked any questions but it did cause me some anxiety as to how I would answer. I had decided if anyone did bring it up I would just say that I had a long drive home. ''
In other situations I generally say "I'm off the booze for a bit. Mid life crisis and trying to get into shape." I'm that "all or nothing" type of quirky person anyway so this works for me.