Congratulations on standing firm! I know I often can't do that :-)

My friend who just drinks Diet Coke now, is depressed/takes depression meds; you could switch to saying something like, "I'm depressed and alcohol depresses one further so I'm doing it for health reasons" or something like that which might make the "desperate" ones who keep trying to make you drink think twice and if they do keep bugging you give them a look like, "do you really want to be asking me to compromise my health? Not a very "friendly" thing to want to do"