Personally, I like keeping even caffeine at a minimum when it comes to me, so anything else (cigarettes, pot, alcohol, whatever) is certainly out.

As for other people, the only thing I actually mind them doing is smoking cigarettes, especially around me. It's strange, but I have one friend who's a smoker, and all of her friends are very chill about drug use -- except for her smoking. I always find it odd that the legal drug is the one we have the issue with.