First, I don't see anything wrong with living a "vegan" lifestyle; I simply love to eat meat. That said, many "omnivores" view vegans as being high-maintenance because they can't eat like normal people at social functions. Vegans are different than vegetarians in that they will not consume ANY animal by-products at all, therefore limiting their choices of foods to virtually nothing. Remember, vegans can't even consume butter, honey or milk. Omnivores (and especially someone preparing food) feel that vegans are an embarrassment when out in public because they have to scrutinize through the menu and are ultimately left feeling dejected when they have to "settle" for limited menu choices. With the exception of one very patient vegan friend of mine, I have never seen a vegan happy with any given restaurant's menu and they tend to irritate the waiters to the point bad service with their complaining. Also, if someone's hosting a party where a known vegan will be in attendance, the host is obligated to accommodate the vegan in regards to the menu making it harder on everyone.
Most vegans I've known seem to "expect" people to go out of their way to accommodate their dietary choices, and are irritable when people don't. Because of this, I will not dine in public with a known vegan because of their negative attitudes towards people who eat like normal human beings. Vegans give themselves the negative stereotypes by generally being impossible to please and irritable dining companions.