My dad thinks he had with people he has never met.

My dad recently has began imagining that he knows Albert Einstein, John F Kennedy, and Franklin D Roosevelt. I try to tell him that he did not know these people let alone go for walks with them, and he just gets either really quiet or irritated with me. He loves reminiscing about the time he and John F Kennedy played tennis in the park and the game resulted in a deuce, He also has ideas about how he helped Franklin Roosevelt with some political business. His stories are so elaborate and crazy that I don’t know what to do.

My dad was an engineer, one of the smartest people I know, and I am embarrassed for him when he talks about these stories and relationships that are so clearly untrue. People look at him like he is crazy and even laugh at him. Has anyone had a loved one with dementia who has experienced this?