I've never smoked because the smell is disgusting, I don't even want to stand near someone who has been smoking let alone actually do it myself. I've always thought it was a vile habit, and kind of stupid... why would you choose to do something that causes cancer? Makes no sense to me.
I've never done drugs because... well I've just never wanted to. I have no curiosity to find out what it feels like, and no one I knew as a teenager did drugs aside for my sister so there was no peer pressure to try it during my more impressionable years.
I don't drink because I don't see the point. I have yet to find an alcoholic drink that I like the taste of (I'm always happy to try), so the only reason I would drink would be for the express purpose of getting drunk... for which I have no reason. I used to drink for that purpose in my first year of uni when I discovered that I love going dancing in clubs and thought from others examples that drinking is a necessary part of that. I later discovered that I have just as much fun dancing sober. Haven't drunk since. It's nothing to do with particularly needing to be in control or anything, I just won't drink something I hate the taste of if it doesn't improve my enjoyment in any way (which it doesn't).
Maybe if I wasn't an aspie I'd be more worried about fitting in and so would drink anyway. People certainly find it weird that I don't drink and like interrogating me about it (apparently '' it tastes nasty'' isn't a good enough excuse

) and some people are infuriatingly persistent in trying to get to have ''just one drink'' *sigh*