I dont know I have a similar issue but with my girlfriend. Ive said so many times I dont like meat I wont eat it I havent had meat in ages that i want to go 100% vegetarian etc etc etc but everytime she always offers me food with meat in it. Every god damn time. Same with my mum and... well everyone I have ever known i wish more people would respect others diets. Your right its really not that hard especially if you are constantly telling the person.
in saying that i try to ignore them as much as possible because its not their fualt they have DEFECTIVE brians :S