What's the worst thing about being told you have Alzheimer's? It doesn't just happen once.
Are you making a joke about how Alzheimer patients regularly forget things?
Because I'm clever and I do my research on it. They don't tell me because they hide it, who would just openly say yes I have Alzheimer's?
Alzheimer's is a terrible mental disorder that causes suffering to the inflicted as well as those close to them. Jokes about such a condition are in bad taste and also mocking to those who have to deal with it. Compassion and understanding for someone dealing with this condition can go a long way in making them not feel hopeless.