Let's get this out of the way, not all vegans are bad. Most of them are pretty educated in regards to their choices and why they won't have animal products in their diet. You can certainly learn a thing or two from the ones that are willing to share their knowledge.
I've learned quite a few things from a close friend of mine that's an editor of an environmental and palm-oil free magazine. I admitted to her that I've wanted to try to go vegan to test my self-discipline and see if changing my diet would make me feel better, both physically and mentally. After talking to her about my concerns, I've decided to eat a mostly vegetarian diet with vegan influences. My favorite thing that she's said to me is, “It's your journey and if you slip, that's your decision and you shouldn't feel bad about your path.” I've slipped a couple time since starting out the diet but she nor any other vegan I've met haven't made me feel bad about it.
Others may not be so lucky. There are those vegans that are preachy and want to make you feel bad for your choices. It's just the nature of the world and those people are out there, ready to make you feel like sh*t for ordering a steak at dinner. They'll have their rant ready to go as soon as you order it medium-rare. There is such thing as being polite or starting an argument with them but the latter sounds much more difficult and you wouldn't be able to enjoy your dinner in peace.