Tell her you are either going to start using a combined mixture of crack cocaine, heroin and opium or take up smoking cigarettes, and then ask her which option does she think you should go for.

You don't. You can't force anybody to agree with your choices, but you can simply MAKE those choices for yourself. That is, despite what those who love you think of it.

I smoke myself, and if my child smoked, I would not WANT them to smoke, and I would not AGREE that smoking is the right choice, but it is still their choice. I would hope that they would take my advice and respond to my negative view of smoking by not smoking. Your mother is trying to help you make a good choice -- smoking is disgusting. It ruins your lungs; it stinks; it puts women (or men) off dating you; it makes you unfit; it can make you impotent; and the worst part of all is that despite knowing all this, it is FUCKING ADDICTIVE and is therefore extremely difficult to give up, even if you know how bad it is for you.

My advice: listen to your mum. Because you might think "aww, I just want to try it, just to see what it's like. It won't addict me". But that's how I started, too. I smoked one, and I liked it, and I though, aww, sure, another one won't hurt. Then it was, "aww, I'll have a few. I can quit any time I want, anyway". And then I tried to quit, and couldn't.

Once you are addicted, it changes the way your brain processes certain chemicals, and once that happens it is extremely, extremely difficult to ever get over the addiction. Impossible for many people.

You get financially independent so you don't need her permission to smoke. Then she'll have to let you smoke.