i used to work with a guy, the kind of pushy, me me me kind of person that gives ny'ers a bad name, who did something once that is still talked about 15 years later as the height of improper behavior as a guest.
my current boss had a bbq at his home years ago, and invited everyone in my dept. out to his new house. (i had to work being the lowest in seniority) well, a few days before the party, this guy's wife called my boss's wife to inquire about what was going to be served. she said that she, her hubby, and their (annoying spoiled) kid were on restrictive diets, and she wanted to know if there was going to be something there for them to eat. my boss's wife told them it was mostly standard american bbq fare, but there were also some salads and other dishes that might be appropriate. the guy's wife then went on to whine about what they could eat, so after seemingly an hour of this, my boss's wife felt badly, and changed half of the dishes she was making in order to comply with this guy's diet.
the day of the party, while everyone was enjoying the modified menu and having a good time, the guy and his family were noticed to be scoffing down all of the snacks, junk food, and desserts that were put out. they totally avoided the dishes that were made specifically for them at their request, and made pigs out of themselves on the least healthy stuff offered. i mean like 2 or 3 slices of cake (each!
even the kid), candies, chips, cookies, popcorn; all the crap you can think of at a bbq.
of course, no one said anything, but he will never live down just how badly mannered he and his family were, and are avoided at all parties at all costs.