what is worse for your health
drugs
fags
alcohol
environment

Environment is the only one on your list that we have no personal control over, so in one way, that is the worst offender. Unless you can go and live somewhere very remote, you will probably be in daily contact with car exhaust fumes, various nasty chemicals and additives in food - some that you will be totally unaware of - and the same in cleaning products etc. You can avoid to some extent but not completely, whereas with the other baddies you mention - alcohol, cigarettes and drugs - it is totally your own responsibility whether or not you take them into your system and risk bad health or even death...I would add sugar, salt and fatty food to the list too. The sad thing is, it is difficult to avoid pollution, and the other things on our list, although we CAN avoid them, so many of us are addicted to one or other of them and cannot resist them even when fully aware of their deadly effects.