If, by some horrid mischance, you find that you have exited the privacy of your home or motor vehicle without fastening the fly to your trousers, one can easily see that you would wish to remedy this situation as soon as it became apparent to you. You may not have noticed while you walked across half of the parking lot; that is understandable.
However, reaching for your crotch and grinning sunnily and lengthily at me while taking a leisurely approach to attending to it is not what we call Minnesota Nice. There are times when a friendly smile and eye contact are truly not called for. This is one.