I read this on another forum. My reaction is "That is completely bonkers!! If people are so particular, they should stay home!!"
But maybe I am a nasty uncaring beast …
On the rare occasions we have people over (like for our son's birthday,) I usually have a large spread of food; most of it is vegetarian (and of that, half is vegan and half is lacto-ovo) and then only one or two non-vegetarian dishes (and those will be made of organic, free-range poultry or fish.) I offer a vegan dessert on top of the cake (which isn't vegan :P) and have ingredient lists handy for each dish I've prepared in case anyone failed to mention they suffer from a food allergy/aversion. There's always also a large beverage selection- from bottled water, fresh-pressed juice, wine, etc.. everyone has something they can drink 🙂
I also am one of those odd people that keep separate pots, pans and cooking utensils for meat, dairy and vegetarian dishes, so if anyone who's Jewish or Muslim should come to my house, they can eat without worrying about violating their food laws (I also keep separate plates, glasses and silverware specifically for such individuals.)