There are various arguments&reasons for vegetarianism:
1) Health; some people believe meat isn't healthy. Some of the arguments using this idea are right, such us very low percent of obese vegtarians and averagely low pressure vegetarians often have; many are fake, for example impotence etc. A health problem with vegetarianism is that an average person gets most of their protein (which we build our cells from) from meat, but it is also to be found elsewhere.
2) Religion; Some Hinduist or Jainist doctrines see eating meat a wrong thing, and so do some of its followers.
3) Dislike the taste.
4) Environmental; it requires more means to grow food, then feed animals with it and then kill them than to eat the grown food itself. Also, the farm animals produce some of the greenhouse gases.
5) Moral; some people see eating meat immoral, because through the act you claim that you agree with killing (or even torturing or somehow ruining its life in case of loads of factory farms) an animal. Moral arguments include "you wouldn't kill/eat your dog", "there is no difference between killing an animal for food and doing so for fun, wh...
person B: So you can't hunt, eh?
Vegetarians tend to be thinner, healthier, and have less body fat than meat-eaters. This is because many vegetarians realize the health benefits to eating a purely meat-free diet and adopt other healthy habits (no smoking, no excess alcohol, regular exercise, etc).
Contrary to popular belief, vegetarians are not preachy. You do not need to 'feel bad' about eating meat around them. They have usually made the choice for themselves and live a peaceful lifestyle that doesn't involve forcing their beliefs down other peoples throats.
No thank you, I'm a vegetarian.
Oh okay, we have some veggie burgers if you would like one.
Yes, thank you very much!
Jake: I'm a vegetarian.
Mark: Are you gay!?
Jake: No you asshole.