The worst-case scenario is that the troublemaker is not just vegetarian but vegan, eliminating a whole range of cheese and egg dishes as alternatives. Things might look bleak. Vegans at cookouts can be walking vials of conversational nitroglycerin, who if riled up can easily spew overwhelming amounts of unpleasant facts about the nonvegan food on your other guests' forks. One who consumes no flesh of animals, including mammals, birds, fish and crustaceans. One who consumes no products of animal origin, including the above, plus dairy products and eggs, and often honey.
Most vegans avoid leather, wool or silk clothing.
Still, these people need to eat, too. At first glance, many people come up empty on this, but actually plenty of foods are left after meat and dairy are eliminated. If you're having just one veggie guest, you could ask him or her beforehand for some preferences. After all, you don't want to slave over a delicious Nam Jim Satay only to find your troublemaking friend is also allergic to peanuts. I, for one, can't stand eggplant.