When we bring a vegetarian entree or a not obviously veg side dish, which we often do and always offer, we also bring, for a buffet, little cards that say "vegetarian" or "vegan" and add "gluten-free" where applicable. We find that non-veg folk often avoid those dishes first time around, and then the cards get lost or moved, and everybody dives in. We bring a lot, because non-veg folk like our cooking, we like to demonstrate that vegetarian or vegan food is really good, and we like leftovers. I do get sick from stealth meat, and usually rope somebody in as my "official taster". It is a good way to strike up an acquaintance, too. It is possible for hosts to reserve and hold back something until all the restricted people have had a shot at it, and then set it out for everyone. That works when quantities are limited.