Yeah that sucks.
I take it case by case but always thinking that the bottom line is we don't NEED to exploit animals, so why should we? There's too much evidence out there proving that living a cruelty free life is healthy for a human being in a 1st world country.
Ultimately, you have to agree to disagree with some people to move on with your day, so calmly saying "I disagree with you" can defuse a person's argument.
I see you are saying being vegan is a personal choice. It certainly is, but not being vegan effects more than just one's own person, but hundreds of other lives, so not a personal choice.
I think Colleen's podcast is exactly for you.
http://www.colleenpatrickgoudreau.com/food-for-thought-podcast/
She has an episode on this very topic about a year.
Edit: This isn't the episode I was thinking of, but I think you might like it anyway:
http://www.colleenpatrickgoudreau.com/10-strategies-for-effective-communication-part-one/