I understand your frustration - when you've taken the time and trouble to cook something that fits in with the guests supposed dietary preferences and they still won't eat it, that sticks in my craw as well.
That's asssuming you have taken that time and trouble of course.
I also have a few food intolerances, they are a royal PITA for many of my friends - but because they are my friends they ask to be reminded of what these intolerances are before I go there to eat, and cook accordingly.
I wouldn't be able to eat a very hot curry/spicy meal - but I would just eat the rice and accompaniments and avoid the hot part, rather than make a fuss.
I would not, however, be able to stomach a fried egg, nor a raw oyster - but these, thankfully, don't make much of an appearance at most dinner parties - I would have to refuse these or run the risk of throwing them straight back up onto the plate (it's a textural thing).
This is another one of those arguments about whose responsibility it is to ensure an enjoyable outcome of an event though, isn't it - as a host, I would do my damnedest to make sure that my guests were accommodated in their preferences; but as a guest I would do my best to eat what they had offered without offending, but also without making myself ill.
If someone insisted I ate what they had cooked, as though I was a naughty child, then I wouldn't ever go back to that person's home again.