Actually, Vegans were easy. They weren't picky, they just wouldn't eat meat. As I had a chef, he had no problems with making vegan meals to accompany us carnivores. As long as they weren't "Separate Galley" type vegans. Or no leather vegans. But they don't dive, I guess.
No, the pain was the gluten free brownie eater or the shrimp scarfing vegetarian. I can't tell you how many times a nice veggie pasta or the gluten free dinner rolls sat lonely and neglected on the sideboard while my "Gluten free" ate their weight in fresh baked dinner rolls, or my vegetarian went plowing through the shrimp.
So I made it easy. If you requested a special diet, we charged an extra fee. Again, Vegans were easy, so they just got meals served to them. Vegetarians were $50, and Gluten free were $100. Kosher and vegan were allowed to bring their own chow if they preferred, and true vegans and kosher can't eat with utensils that have touched the "unclean". That put an end to the gluten free and shrimp eating vegetarians.