I'm semi-vegetarian in that I'm pescetarian. Basically I'll eat plant foods, no-kill animal products (like eggs, milk, honey, etc.), and seafood. I'll also eat occasional meat if I'm in a situation where not eating meat would be a breach of hospitality, though that really only happens around certain holidays.
I've been vegetarian off and on and to different degrees for about 15 years now. Mostly it's a health thing for me -- my family is prone to heart problems, diabetes, and blood pressure issues, and a vegetarian or pescetarian diet can help improve things in those areas -- though in the last few years I've become more interested in eating a less processed, more locally sourced diet. That's how I got interested in keeping chickens, as well as gardening, and how I got connected to a local farmer from whom I buy milk, etc. I kept seafood in my diet for the long-chain Omega-3s, as well as so that I could still have convenience options when traveling, and so I wouldn't have to give up sushi, but I don't eat it very often. That said, this summer I'll probably do a little bit of fishing in order to gather some of my own fish.
But yeah, my friends and I joke a lot about how delicious my future chickens aren't allowed to be.