My mate Pete has recently been diagnosed with dementia. We now call him Repete. Also works with Dave, we now call him Dave ja vu.
Are you trying to make fun of dementia?
In fact, dementia is an irreversible disease. Instead of calling them patients, I call them patients because they are unable to remember. It's funny that they repeat what they say everday.
It's not very funny to joke around about dementia patients. Please try and understand why your words could really hurt a dementia patient's feelings.