I'm a newbie and this is my first post but, what has worked for me in my particular "social circle" is to throw a little comedy in it (especially for those who were used to seeing me with a beer in hand, now a diet coke).
I simply say "No thanks, I've decided to give my liver a break". I get a chuckle and often a "good for you" (very rewarding) and then go on with a good conversation. Nobody thinks twice about it.