Carolyn, a rich blonde, buys a new automatic Jaguar XKR Sport. She drives the car perfectly well during the day, but at night, the car just won't move at all. After trying to drive the car at night for a week (but without any luck), she furiously calls the Jaguar dealer and they send out a technician to her.
The technician examines the car and finds nothing wrong with it. So he turns to the blonde and asks, "Ma'am, are you sure you are using the right gears?"
Full of anger, the blonde replies, "You fool, you idiot, how on earth could you ask such a question? I'm not stupid you know! Of course I am using the right gears; I use D during the day and N at night."
Stolen from: Jodi of Jodi's Journey