Where do we draw the line on sin?

I just asked a question..somewhat related and I forgot that when you ask a question about yourself personally, only people who know you or get you somehow can give you accurate perspective so heres another take..As a Christian, I know that Jesus will forgive my sins but there is a but involved. You can't just do the same thing over and over again and just keep asking for forgiveness, you have to actively try to resist temptation. So as a Christian, what is sin in specific situations? Is going out to night clubs or bars sinning even when you know that you won't end up doing something really stupid ( with a stranger etc?) You still dress and dance provocatively and make other people want you in that way. But we are lustful creatures at the same time. Drinking but in in a controlled situation? And if drinking is ok, then why are drugs so bad (Don't get into the legality of it, simply the drugs itself?)