What are the main things that are bad for your physical health?

The real dangers: Smoking. Hard drugs like meth, any opiate, cocaine. Alcohol in excess. Lack of exercise. Excess salt. Not using sunblock. Getting vitamin d deficient. I would rank the other things you've been warned about -- refined sugar, red meat, greasy stuff, smoking weed, trans fats, all below the one's i've listed. Others may disagree. Trusting you get enough sleep and will practice safe sex.

Tobacco: Using tobacco products is one of the worst things that you can do for your health.