It really sucks that this is happening... Like others have mentionned, having a good talk with your dad is definitely in order. Hash everything out and don't let it just be done in a few minutes. Find a time and place where you can talk with your dad alone for an afternoon and evening just the two of you.
It sucks that it seems to be the smoking issue that is causing this rift but I can understand where your dad is coming from especially if he used to be a smoker himself. He's personally lived through the addiction and finally was able to kick it only to see you doing the same mistake he did... A parent only wants the best for their kids and this is a situation that I would imagine is quite hard to deal with...
I think he doesn't want to be "okay" with your smoking habit for fear that it would be a form of acceptance from him. If he lets it slide it would mean he's fine with it which he's not and I think he just doesn't want to give you that message ever. I can understand that....
You say that you've tried to stop smoking but can't... I know it's hard, trust me!!! I'm tackling that battle shortly after being a heavy smoker for more than 15 years. If you think it is a tough battle now, it only gets harder and harder the longer you wait.
I really don't want to sound preachy about smoking as it's a personal choice and battle for each of us. But you are seeing a different side effect from the habit that you didn't think would happen and that just goes to show you that it's just not good from whichever way you look at it. There are consequences that reach farther than the health aspects of it.
I myself feel embarrassed about my habit when I'm with non-smoking friends. I have to make them wait for me while I'm outside puffing on my smoke because I can't wait, and then I come back in all smelly... Can't be too pleasant. The fact that they worry about my health just makes it even more embarrassing because I know that they are right.
I wish my parents wouldn't have accepted it when I started as it might have influenced me to stop it back then and not get into the mess I'm in now with cigarettes... Don't know if it would have worked for sure but it would have been nice if they would have put their foot down about it and stuck to their guns about how they felt about it.... Personally, I think it's a good incentive as I don't think I would have let my relationship with them suffer because of it...
You have two battles to face... Trying to fix your relationship with your dad and to stop smoking...
I wish you the best of luck in both
Keeper of 5 snakes, leopard geckos, 1 green iguana, 20+ tarantulas, 2 dogs & a bunch of rats!