When I got to work yesterday, my very first customer was a very old man, 'bout 150 or so, who mumbled something about a latte. Since I wasn't sure whether I heard him correctly, I repeated his order. He then gave me a look that I haven't seen since my Dad was teaching me how to drive, and said, "Are ya stupid, boy?".
My response was to smile (as stupidly as I could, which isn't a stretch), drool a little, and pick my nose. The look on his face kept me going the rest of the day.
As a young man, I probably would have handled it rather badly. I'm older now, and my skin is a little thicker.
The moral? Don't sweat the small shit. Have fun with it.