Heh. Imagination suppressed.
Alex's comment is right on point. I have found that the more specific I am, the more likely the message will get through. I have often said "my son and I are allergic to milk - if this item has any milk in it, or anything that was made from milk, one or both of us will stop breathing and you'll be calling 911."
Blunt. To the point. But for those waitpersons who said "no" when they were thinking "how could a little hurt," they immediately think twice and go talk to the chef.
Mark

 A somewhat more effective statement is "if my meal as much as comes in  contact with any milk-related product, in 10 minutes you would have
 paramedics giving me CPR. By the way, I am not sure that the other patrons would get the right message..."