Why do vegetarians talk about being vegetarian?

It depends on why they are vegetarian. If they really cant eat meat then I wouldn't know why but if they chose to be vegetarian then they most likely don't like eating dead animals.

A second viewpoint:

Vegetarians comprise a broad variety of personality types, many of whom do not complain at all, but rather just want to live their own lives without judgment. There are many reasons people may become vegetarians--health, religion, treatment of animals, eco-efficiency, or others. There may be a correlation between personality type and the political aspect of a particular vegetarian's reasoning.