From The New York Times.
Dear FloFab: My Waiter Joked About My Food Allergies: Q: For people like myself with food allergies, going out for dinner requires a bit more research, such as viewing the menu online and calling ahead. I also attempt to choose dishes that would be easy for the kitchen to accommodate — for example, by leaving off the sauce. But how do I handle a wait person’s rudeness when he or she tries to belittle my request in a loud enough voice to catch the attention of the rest of my dinner companions? (“Oh, it only has a little butter — what’s the worst that can happen?”) I’m dying for a witty retort, without having to lay out a medical explanation, to keep the attention from being on me. Flo says talk to the manager. Read Flo’s full reply here.
My reply: you never had to put up with rude behavior, ever.
My best suggestion: before you sit down to diner, talk with the manager. Let the manager inform your waiter of your dietary needs (off stage, as it were). By the time you get to the table, there's no table-side discussion or chance for rude remarks.
However, if the manager gives you the same rude questioning treatment (because guess who trains the staff) then do not patronize that restaurant. Don't get angry, just take your business elsehere.