Dealing with the assholes...
Sooner or later, you will come across someone who doesn't agree with you. Not all of them intend to be assholes, many are well-meaning, like, family type people who are concerned about the amount of protein you're getting, or are just confused, whatever. Some do intend to be assholes. These are the people you have my permission to hit.
These are things that people have said to me or friends of mine when trying to convince me or them that being a vegetarian is stupid:
1. The animals are going to die anyway.
2. The animals are going to be eaten anyway.
3. The animals were raised to be killed and eaten, and if that hadn't been so they wouldn't have lived at all. (would you want to live, knowing you were only alive to be killed and eaten?)
4. The animals don't know. (how about you switch places with them and see how quickly you figure it out?)
5. Animals don't have feelings. (wait a second, aren't you an animal?)
6. If we weren't supposed to eat animals, why are they made out of meat? (this one is so stupid it amuses me. So are people, genius.)
7. But they taste so good! (asshole.)
8. Many companies (or whatever you want to call it) kill the animals as humanely as possible so they don't suffer. (oh really? Refer to #4.)
9. But it's all true. (above reasons ^. And I don't care.)
10. Then why are you eating eggs? (I'm not a vegan, dumbass.)
11. For every animal you don't eat, I'm going to eat three. (Maddox)
If you find people saying these things to you (or any other anti-vegetarian BS), just make it clear that you don't care, this is the lifestyle you have chosen to live, this is what you believe in, and you aren't going to change your mind; or say something similar to what I put in the parentheses. That's what you do the first one or two times a person says these things to you.
For repeated offenders...if you're friends with them, just smack them upside the head. This usually makes Josh shut up, and just threatening Dave will make him shut up. You'll have to find out what works best with your own friends.
If you're not friends with them and/or don't know them well, just keep politely reminding them that this is the lifestyle you have chosen to live, this is what you believe in, and you aren't going to change your mind. If they don't get the message after, say, ten reminders, then you can smack them. They deserve it.
And then there's the people who, once they find out you are vegetarian, think it'd be funny to try and get you to eat meat, or shove a piece of meat in your face, or leather jacket, whatever. These people are not well-meaning, they're just assholes. You can hit them right away, regardless of how well you know them or whether or not they were joking. It's not funny, and it never will be.