If you're like most people with a GPS, you've probably yelled at that smug little voice that seems to know so much more than you do about how to get from point A to point B. It may be that the voice is just too chirpy, especially if you're in a bad mood:
"If you think about it, when you're happy, you want to be around happy people. But if you're sad, do you really want to hang around chirpy, happy people saying, 'Let's turn that frown upside down?'" said Clifford Nass, a Stanford professor who studies computer voices. "No. You want to punch them."
Why GPS voices are so condescending [CNN.com]