Whether for healthy, religious, ethical, political or allergy reasons, it seems like there are limitless possibilities for what people won't eat. But as a host you can serve whatever you want, right? Well, sort of. It's your party and you can fry what you want to, but a good host also tries to make her guests feel welcome. Here are some tips for being a considerate host without having to act as short order cook.
As a host you need to accept that vegetarianism (not eating meat) is pretty common nowadays, as a result you should always include meatless items in your menu. The only exception a small sit down dinner party where you know all the guests are omnivores. However, when serving a crowd you should plan on there being at least one vegetarian. Luckily, this is one of the easiest restrictions to accommodate.
First, make vegetables vegetarian. We omnivores sometimes use bacon like a seasoning, which can result in many dishes that feature vegetables but aren't vegetarian. Indulge your pork addiction in close company, but when serving a crowd leave the meat out of anything that features vegetables. Don't forget to replace any chicken or beef broth used in the preparation.
Portion your vegetarian dishes with the expectation that not only vegetarians will eat them. Remember that your other guests are likely omnivores, not strict carnivores, which means they'll eat some of the vegi stuff too. My graduate school included a lot of vegetarians, so at events there would always be a vegetarian option (usually hummus). Unfortunately, because the hummus didn't need to be heated it would come out first and hungry students of all dietary ilks would descend on it. As a result, late-comer vegetarians were usually left with nothing even while piles of chicken wings and roast beef sandwiches remained. If you have delicious vegetarian options your other guests will eat them, so be sure to have extra. The good news is that most vegetarian options will be cheaper than your meat options.
Assess the vegetarian options as a menu. You think you can buy a vegi tray and be done with it? Maybe, if you're only serving snacks to everyone else. I've often heard vegetarians complain that they feel like they are eating the garnish. Offer your vegetarians a variety of substantive items. You don't need to go one for one with meat dishes and vegetarian dishes, but if everyone else is getting a meal the vegetarians should get more than baby carrots.
What if you have no idea about vegetarian dishes? If you know a vegetarian on your guest list, ask for suggestions or for them to bring something. They'll likely appreciate that you are thinking of their needs and be happy to help. Otherwise look for recipes online. Or check stores. Middle Eastern delis often have a variety of delicious options.
Other Dietary Restrictions
In addition to the basic vegetarian meatless diet there are a multitude of other potential food restrictions. Some people will only eat fish. Some are vegan (no meat OR dairy). And then we get into the worlds of gluten-free, lactose intolerance, kosher, halal, low carb, low fat, low sodium, food allergies and so many other dietary variants. As a host you are not expected to compensate for these unless you know that one or more guests eat a particular diet. Many times you will have fore knowledge of a friend's diet. Sometimes you may not know prior to the invitation in which case it is the guest's responsibility to mention it before the event. In either case there are 3 main ways to handle the situation.
1. Accommodate the guest's diet. Sometimes this is easy. For example, if someone is allergic to shellfish but you weren't going to serve any there isn't a problem at all. For other situations a small tweak to the menu will solve the problem. Occasionally the dietary restriction will require significant adjustments to your menu, but you may be willing to make the effort in order to not exclude someone.
2. Ask the guest to bring something. Say that although you won't be serving anything (or very little) that they'll be able to eat, you still hope they'll be able to attend. Unless it is a very large party you should suggest that that they bring something to share rather than just something for themselves. Particularly if people are sitting down to a meal having a shared dish will help keep the restricted guest included in the community of the meal even if others are only taking polite spoonfuls of the special dish.
3. Apologize for not being able to accommodate them. If it makes sense you can invite them to come later for dessert or drinks. Otherwise suggest that you get together at another time. It's okay to not want to change your plans particularly if for only one person (particularly if it is someone you don't know well). If you were throwing a party on a boat you probably wouldn't cancel just because one person is afraid of water. It's your party. Although it is nice to be inclusive there are limits. Most people with particularly complex dietary restrictions understand that.
Label Your Food
Even when you aren't knowingly dealing with dietary restrictions guests appreciate knowing what they are eating. If everyone is sitting down to dinner together you can explain each dish at the table, but if people will be grazing it is helpful to label anything that is not obvious. Write neatly or use a computer to print small cards to set near the food. Fold the cards so they stand up or use wire photo holders for a fancier presentation.
The Omnivore as Guest
So does it work the other way too? Can an omnivore demand meat and fried potatoes? Sorry, but no. If the menu is within the set of things you can eat it is rude to make demands of the host. If you won't be satisfied with the meal you'll get at the house of a vegan raw foodist sneak out for steak later or decline the invitation.