Tobacco smoke is full grade A carcinogens. Like with asbestos (another grade A carcinogen), there is no safe level of exposure. Also, carbon accumulates in your lungs. Ie: it never leaves. And can cause black lung, COPD, emphysema and many other problems.
Alcohol is a universal poison. It kills everything. Small amounts aren't likely to cause serious injury, but to say that it has no effect is wrong. Besides the damage to your tissues, alcohol can totally fuck your metabolism and your endocrine (hormones) system.
No, drinking alcohol once a week won't damage your gains. Just don't smoke, quit smoking forever. I'm also struggling with my tobacco smoking habit. It makes your blood thick, decreasing blood circulation which results in weaker erections. Drink a lot of water!