The second worst thing about being a vegetarian is going to a restaurant with a group of people where there is a single vegetarian item on the menu and finding that several of the non-vegetarians at the table order the vegetarian option. The sophisticated thing to do would be to order something else, only you can't.
The worst thing is the eternal guestion, "why are you vegetarian?" I try to be honest these days and say, "frankly, I can't remember." But that isn't really honest. It would be more honest to say what I'm thinking which is, "none of your fucking business." It's not a lot different from asking somebody why they are Christian: a reasonable question for a friend to ask but impolite for a stranger to ask. There's no simple answer, and the question (when posed by a stranger) assumes there is. Conversely, a friend has context, understanding, and genuine interest.
As a vegetarian, in my experience it is an impossible question to answer. You can't answer it in a way that doesn't make you look bad, while at the same time (if you're me) you're trying very hard not to offend somebody by sounding judgemental.
If you try to justify it morally, then you may encounter the argument that "at least the sheep had some kind of life" or "what are your shoes made out of?" (mine are leather). I used to argue that if I wouldn't kill the animal myself then I shouldn't eat it. Shoes are of course the Achilles heel of that argument too, so I don't bother any more. It's very hard to justify vegetarianism like that. People may as well just ask, "Why are you such a hypocrite?" But that's the thing. I would only have to justify it if I were applying my personal morals to others. Sure I'm squeamish about seeing friends put big chunks of cow in their mouths, but I'm not judging them for it. I just avert my eyes as necessary. I do wonder why it bothers some meat-eaters so much. I suspect they think vegetarians are angling for some kind of higher moral ground (which is how vegetarians think about vegans, those weirdos) and so are adopting the philosophy that the best defense is a strong offense.
I guess the best way to describe being vegetarian in a non-judgemental way is to say that I feel the same way about eating a sheep that a non-vegetarian might feel about eating, say, a cat or dog.
I interests me that the distinction between which animals are food and which pets is culturally determined. Because let's face it: they're probably all scrumptious.
Farm animals (pigs, sheep, cows, chickens) are smarter and more emotional than people like to think. Pigs make good pets (council bylaws notwithstanding) and are generally considered to be as smart as dogs, yet we see pork. Sheep form friendships and can recognise the faces of other sheep over extended periods of time [link] — lamb chops. There are stories of cows using their tongues to open gates in order to be reunited with herds and calves — steak. And finally, chooks are often kept as pets, and are quite capable of bonding with an individual human — McNuggets. Somebody should write a book about how smart food really is — it could be a beast seller.