I agree with Ytterbiumanalyst. Correct me if I'm wrong, but I believe that's exactly what St. Paul was talking about in Romans 14:1-13. Sin is what I do against God's will, or, in other words, what I do that makes me not God's. If I drink in moderation (or, in Paul's words, "eat everything"), but drinking does not make me a godless addict, then I am still God's and, therefore, my drinking is not a sin. If I become a drunkard when I drink, then it's better for me to abstain from drinking (or, in Paul's words, "eat only vegetables").