I flipping HATE that.
I'ver had that loads of times, once a passerby (not a customer lol) said it to me, and I couldnt help myself. I said "really? You think so eh? Do you think I had a choice about what days I work? This is my business.
Yes I may have PICKED a good day to clean windows, but you also PICKED a good day to be a moron"
I said the last bit under my breath of course!