"Have you gone to the dentist today?" "No no, you should know he was the classmate of your father."
I have this kind of conversation with mother every day. It doesn't mean we are insane, just means my mother's hearing is quite bad (though except it she is very active & reasonable for her age). If I need the proper answer then usually I can get it when I ask the same question again or 3 times. But most of time I don't want the real "answer", it's just a casual conversation, so it looks quite ridiculous to ask her the same thing several times.
And when I'm tired after the long work hours, after hours suffering from headache all day, her off-the-point talking often irritates me. I know I have to be tolerant. We can't help it, anyone can be the same when they become 78. Still... (sigh)