My Grandmother: "Turn off the fan, you're going to catch a cold"
Me: "But temperature doesn't cause sickness, germs do"
My Grandmother: "Don't tell me what makes you sick, I've been alive longer than you have"

This coming from the same person who leaves the microwave door open after using it to give it time to "cool down", since she thinks that it cooks food using heat in the same way that an oven does.