It's the same way people get defensive when someone else says they're a vegan. People may often take it as this person signaling something they do as 'normal' and your refusal to partake means there might be a health, moral, or other flaw in their practice. That someone else never said anything further, cast down on the questioner for drinking/eating meat/etc., or said "it's debate time", but it's the symbol that the very thought that maybe they should second guess themselves that disgusts them -- and this event was supposed to be fun, and you are making it serious.
I guess the pro-tip is to always have non-alcoholic beverages at a gathering.
There are teetotallers, and then there are teetotallers. There are vegans, and then there are vegans.
I lived in Manhattan for just under 8 years, and have been in Hong Kong for almost 9 years now. I have more friends and colleagues who are vegan here (and a few Jains), but I've never seen the social posturing here that I would sometimes see from vegans in NYC. I don't mean to imply all, or even a majority, of teetotallers, vegans, etc. are virtue signalling in New York, just pointing out the near complete absence of posturing and virtue signalling (at least over those choices) here in Hong Kong puts New York in sharp contrast. I took my wife to New York for the first time a bit over a year ago, and our AirBnB hosts were way over the top sharing their dietary choices, to the point is was very confusing to my wife. I had to tell my wife something along the lines of "Don't worry about it. These aren't actually super strange people. It's just something some people do here. We don't have to worry for our safety." We have vegan friends and colleagues here, and my wife's sister-in-law believes in a branch of Buddhism that doesn't eat beef, but posturing over dietary choices was completely foreign to my wife.
My weirdness was that I didn't own a TV for about 10 years prior to getting married. I understood a lot of people who didn't own TVs were really annoying about it. I presume not owning a TV is too passe as a virtue signal these days. With me, it only came up if someone asked me what I thought of the latest episode of XYZ.
Anyway, I see huge differences between New York and Hong Kong about how people present that they don't drink alcohol, are vegan, etc.
I think certain people are desperate to create an identity because they rejected their past identity (became atheist for example). I don't really understand why people are so militant about these things either. I don't drink normally but I'll drink on occasion (with my colleagues for example). Because of this I never get questioned if I decide to stick with water on a particular occasion. My colleagues don't feel like it isn't perfectly valid and it requires none of the (perceived) virtue signalling on my part.
In my experience people get annoyed at hanging out with (the more intransigently judgey type of) vegans because it radically limits the possible places to go eat, and it can get tedious hearing a moral lecture at every available opportunity. I’d speculate that some vegans need to constantly talk about their veganism as a way of suppressing their own uncertainty about their decision. [Not unlike people who have adopted other causes as a core part of their identity; vegans are hardly unique here.]
I’ve never seen someone get mad when a vegan e.g. brought their own food to a social gathering, or directly answered questions about their experience of veganism.
I don’t really buy this explanation because vitriol against vegans is alive and well even in regions and communities where vegans are effectively non-existent. N.B.: I grew up in rural Wisconsin and have never knowingly met another vegan in my life.
>some vegans need to constantly talk about their veganism as a way of suppressing their own uncertainty about their decision.
I met up with some friends in a park recently. It was hot so I suggested ice cream and one vegan dude I'm not that close with comes with me to get it. As we are walking back I notice he is eating an ice cream which is weird cos he's vegan. Without me prompting he says
"Oh damn, I forgot I was vegan"
Then he goes on a monlogue about how he's been feeling so good since he became vegan and he thinks it's great but he sounds totally unconvincing. Like he doesn't believe himself. Later he pulls some pre made vegan food out of his bag and slowly starts eating it. Turns out his girlfriend packed it for him. I talk to some friends about it later on and they inform me that he regularly cheats and pretends to himself it was an accident. Dude is probably malnourished and under the thumb of his vegan girlfriend. It's kind of sad.
Or when you say you don’t intend to get married. They take it as a personal attack on their decision to get married when it actually has nothing at all to do with them or their marriage. Even the most progressive people can be weirdly defensive about the cultural norms they’ve adopted.
I guess the pro-tip is to always have non-alcoholic beverages at a gathering.