While everyone is saying that your family cares about you and stuff, whether this is what prompted your sister's snooping in your stuff is debatable. You haven't really said enough about her for me to make an assumption that she was trying to help you or that it was out of caring. My first impulse would be that with someone that cares about their sibling, especially a younger one is that they wouldn't snoop at all, but actually talk to them directly about it if they knew. The behavior screams loudly of her motivated to do something to get to you or get you in trouble, hurt you or something that doesn't seem all too supportive of you in the first place. People don't snoop to help or support their loved ones. It's just not typical behavior. Do you and your sister have animosity between you right now? Is she angry with you for something recent? I just can't say for sure based on the brief information of your family and especially your sister.

Your dad's reaction, albeit more overboard than necessary, could easily be taken as anger, not at you but at finding out that his daughter is doing something that is risking her health. I can't condone his storming off like that and lashing out but on this front I would let the dust settle,let him calm down and talk to him about it. I would venture to say that he just plain doesn't want you smoking. It would be a frustration as a dad to find out, especially when you are of legal age and he knows that you're at a point in your life where most kids start spreading their wings. He's dealing with his daughters becoming adults and that carries a lot of stress in and of itself without having to deal with thinkng about them doing things that are health risks. Try to understand from his perspective.

No you're not a bad person, you're a normal person, with a habit that is unhealthy.

Talk to your sister. Call her on the snooping and confront her. Draw the line, and make it clear that snooping in your stuff is over the line. You probably assume that she knows where your lines are drawn but by verbally confronting her and telling her not to do this, you put the ball squarely in her court. If she does it again it's a clear disregard for your personal space. Findout, if you can, what her motivations are that made it so she thought she had to sneak about to and "tattle tale" on you -- yes, that's what it really amounts to and she sounds very immature for being your older sister!

Hope this helps!
S4