There are a lot of events that make being vegan inconvenient. I value myself by going out and having a good time with friends. Sure I can tell my friends and family to fuck off, but that sounds miserable.
Just don’t eat at the event. I’m not vegan, but I do eat fairly healthy. When I’m traveling and can’t find something that fits healthy I just go without. If your friends continue to bring it up and give you a hard time then they are not your friends.
Well if they're REALLY your friends they shouldn't care to begin with. I'd say only 1-2% of interactions out of hundreds result in people saying anything. Not even that many people joke about it.