People like to include others socially in their good or bad habits. If I take a straight look at myself and I'm cooking healthy, I like people around me to enjoy that healthy food with me. Same as when my friend who is a heavy drinker comes to stay, she wants me to drink with her - but her drinking actually makes me want never to touch the stuff.

I think it's a boundary vs reaching out and belonging issue, and there are ways to connect socially without adopting other people's bad habits. For example, I used to bring a healthy snack = fruit/ dried fruit/ when other people were eating sweets.