Admittedly, I'm not vegan, I am vegetarian. But I still do have some insight onto this topic.
I don't really agree with the idea that vegans (or veggies etc) constantly nag people about their dietary choices. However I completely understand why some people might, because it is a very controversial matter since it's tied so close with morality.
Personally, I don't bring up my being a vegetarian out of the blue unless it is brought up by someone else. I accept that other people might want to eat meat. I can't change their minds. I only ever "nag" my sister or my dad, but that's more of a light-hearted issue and they both agree with me anyways, LOL.
I think a better topic for this thread could be about why meat-eaters are so defensive of their dietary choice when it comes to a few small comments from people who decide not to support the killing of animals for meat? Perhaps, on some level, you don't want to admit that you agree with the blood-shed of millions of innocent creatures for your temporary, selfish and thoughtless pleasure because, really, you know it's not exactly justified.