OK - Only to be used if they have an invalid, completely fatuous request, observation etc.
Window Cleaner: - "Excuse me madam, have you got a face-mirror in your handbag?"
(Ex) Customer may say "Yes" or "No" to this, it doesn't matter.
Window Cleaner:- "Oh good!" or "That's a shame" "cuz I wanted to check my forehead and see if somone had written "Stupid" on it."
(note to Tosh:- this works better on the ladies unless you want to lose another pair of front teeth

)