You see, both people you'd do that too have amazing resolve to abstain from things that are no longer part of their life. If a vegan can be tempted by an edgy kid eating a cheeseburger or an alcoholic tempted by a belligerent asshole waving a drink around, then they really don't have that conviction down yet. Meat is everywhere, as is alcohol. So if a vegan or an alcoholic wants to choose to change their lifestyle, it will be by choice. If you think vegans salivate when you have a steak or an alcoholic is frothing because you have a drink, then you obviously don't know any. And if you do but rarely see them, they probably just dislike you as a person, and not because you choose to eat meat or drink in front of them.