...when a mosquito bites me on top of my head. Oh..? not literally. I scratch my head when I observe rude behavior, like smokers who throw their butt on the ground just before entering a store. People in supermarkets who leave their cart on the right side of the aisle while they are looking for something on the left side and you can't get past them. Then when you say excuse me, they look at you dumbfounded as to what you are attempting to do.