I just wondered what other people do, as I dont think I know anyone who doesnt drink.
I don't drink. In fact I never have, with the only exception being when I was 6 and asked my Dad what beer tasted like. I'm 32 now and I still remember the flavor... I remember it being pretty good actually!
(If you don't want the story, skip down to the ***)
Anyway, before anybody freaks out, let me explain, because there are multiple reasons behind it. About that same time period as a child, I became aware of my older brother's battle with addiction... to everything he could get his hands on. He was 16 at the time - he's 42 now, and has within the last 5 years finally achieved sobriety. Early on, I "vowed" never to go through that, and so, when I hit my early teens, I was one of those annoying kids who wouldn't do anything remotely illicit, and would actively rag on anyone who did. Douchey McGee!
As I got into my late teens, I started to grow up and see the judgments I was making, and how they were affecting my friendships. I softened my stance in terms of what my friends were doing. But then I was first on the scene at a multiple fatality car crash that was definitely caused by a drunk driver (who eventually went to prison for vehicular manslaughter) and while I'm aware now that that was a highly unlikely and extreme example, it still really made me shy away from wanting to partake myself...
It's funny because, as an actor, all through college, grad school, and into my professional career, I've been surrounded by the stuff! (Everything you can think of, believe me.) At some point, somewhere in there, it eventually developed that the idea of doing it just didn't excite me enough to go ahead and do it. Now, that said, this may just have more to do with me as a person; I'm a little wacked-out and crazy anyway! I've been the one dancing on the table with the lampshade on my head with nothing in my system. I've found myself in plenty of trouble as a result of my general willingness to make a complete ass of myself. I don't need to drink to "loosen up" or "be social," you know?
Haha, I read the line above and it sounds like a DARE ad... geeesh... anybody remember those?
I certainly don't judge anyone's choices anymore; I don't believe any kind of state-altering substance is inherently a bad thing; it's just not-so-healthy for some people! A lot of great art has come from a good bender or two. Two of my dearest friends are WAY more fun when they're stoned or drunk! In fact, I am a supporter of pot legalization. (Fun fact: my grad school was the first to successfully produce synthetic THC.)

I just don't do it myself.
*** So, how do I deal with it in public? Eh, all of my friends already know I don't drink and they don't make a big deal about it. On those rare occasions someone asks me why, I usually make the joke that I'm not yet old enough to drink (which is doubly funny because my gf is quite a few years older than me, so it makes her look even more cougariffic!) The "Designated Driver" comment is an easy one too (though here in NYC it's more "Designated Walker.") In general, I've found people don't seem to think much of it after the initial encounter. If you don't make a big deal about it, other people usually won't. People will make their own assumptions, and they'll usually keep them to themselves ... and you can just let them keep thinking what they think, if you choose to. If they ask, I say tell them honestly - and as for anybody who rags on you or won't let it go? Well, I would re-evaluate why they're in your company...

LOL.