I recently had experiences with a regular social group that demonstrated this. It's a group that drinks regularly except for two people who don't. One always

I recently had experiences with a regular social group that demonstrated this. It's a group that drinks regularly except for two people who don't. One always feels like he fits in fine, while the other's presence always stuck out as not fitting in. I had to put my finger on why to tell him, after a few events where I found myself not desiring his presence and deliberately hadn't invited him. I'd peg what's missing as vulnerability. Alcohol lowers one's social filters and inhibitions, of course. All the rest of a drinking group is participating in that shared experience, of letting inner thoughts and feelings be more exposed. The risk of saying or doing something one might later regret is part of the thrill. "Having fun" is the euphemism for allowing others to see that state in you. Some people can naturally achieve that vulnerable "punch-drunk" state without alcohol. Some don't. A person who doesn't inhibits that whole vibe for everyone. You're not a peer, you're a monitor. Doesn't matter if you say you don't care -- the reality is that you will resist getting drawn in to whatever excesses are happening, and everyone will perceive that resistance and themselves adjust for it. Your presence of not mutually participating in the vulnerability drags down the vibe for everyone. It's not exactly the alcohol, it's the state of mind, but of course there is a correlation. Of course this depends a lot on the nature of the social group. A college fraternity will just plow ahead and ignore that resistance. A country club probably has everyone acting restrained enough so as not to clash with one more reluctant personality. But there are those in-between groups, with social barriers high enough to exist but low enough to be pierced by alcohol, and the presence of a nondrinker acts against that piercing that the participants seek.