As a non-drinker/smoker/promiscuous, I get this question a lot and I always think its stupid (no offense to you for asking, I just think the question is awful).
A vice is something that you know is wrong, but you do it anyway because you enjoy it. Drinking alcohol isn't a vice (for adults, I guess). There's nothing morally wrong with drinking or doing drugs or having tons of sex (unless you're a puritan). Yeah, drinking alcohol may not be "healthy," but neither is drinking Pepsi or eating ice cream. Those are hardly vices.
What's your vice, blokeybloke? The real vice, not the "vice" that you do on the weekend, in public, in accordance with the law, with friends and strangers, but the thing you do in private, at 3 in the morning, that you enjoy more than anything, but have never told anyone you do because it's either too shameful or too illegal or both. That's a vice.