“Can I help you please?”
“Yes, could you please put this roll of film into my camera?”
The customer hands over the most expensive 35mm camera at that time. A moment later everything is done.
“Excuse me, Sir, I don't mean to tell you how to take care of your camera, but I couldn't help notice that your lenses are rather dirty. All the extra performance that you spent so much money for certainly gets lost that way.
“Oh no, that's alright. Someone who knows told me the best way to keep a lens clean is to lick it...”