Some people do feel the need to make excuses not to drink--especially in early sobriety.
There are a few problems with excuses, IMO. One is when you run out of them. What if one of your friends had informed you that he or she couldn't drink because of prescribed medication, so they were willing to be the DD, and you should go right ahead and enjoy yourself? Another is that we are continuing to be dishonest about our sobriety, just as we were about our drinking problem. In general, I think we want to be working toward honesty, not more dishonesty. That doesn't mean we have to explain that we are alcoholics (that's nobody's business unless we choose to share it), but what's so bad about simply saying we don't drink, or don't drink anymore, because we've decided it isn't good for us? Saying it's for our health is perfectly true, and something that shouldn't engender any debate.
I'm not trying to be critical of what you did, Bob, just questioning whether in the long run it's a great idea.