Since we're in the minority, everyone new we meet has a habit of trying to challenge us...
Because it's their chance, finally! "I've never met a vegan before! Now is my chance to stereotypically argue and prove them wrong!"
It's funny because it's their first time at bat, and we're like experienced pitchers.
Same stuff every time.
Oddly enough, as a vegan I've found that the stereotypes for vegans are completely manufactured by omnivores. I don't storm into every McDonalds I see to try to educate people. In fact, I never say anything unless I'm asked a specific question.