Elle - I totally know where you're coming from! It's even harder when you have to explain it in another language. DP's family in Lebanon think I'm a freak, but it's pretty easy to over-eat there and still be vego. Not so easy in France, tho, as they're a very meat-centric culture. I carry an international vegetarian card in my wallet now, with "I'm a vegetarian, what can you recommend?" in about 20 different languages, and pictures of animals and eggs crossed out on it!
Here in suburban Oz it's a different story, and people just don't seem to know or care about where their food comes from, and will eat anything out of a packet and expect you to do the same.
I would be making an effort, for your own health too, to make some really nutritious and delicious vego food (it's not that hard - really!), and take some with you next time you have to visit. Make enough for everyone to try it at least, but don't mention that it's vegetarian. Vegetarian does NOT equal bread and salad. At least not their notion of it.
Just my opinion (and I have a few of them... ) but I always get some smug satisfaction out of eating something fabulous that I've brought along to one of those situations, because my food is a pleasure, not just badly cooked meat.
ETA - snuggly, we posted at the same time! I can't remember the last Ekka I went to, but I wish I had one of them kewpie dolls on a stick... that smugness is hard to beat, hey? When you lift the lid on something really awesome, and then don't have to share it!