'Wear a smile and have friends; wear a scowl and have
Not all smiles betoken pure-minded kindness, generosity and warm-heartedness. There will be feelings of undeniable cynicism about the vulpine smile of the salesman as he hovers on the edge of a deal, the insincere grimace of the flight attendant as she doles out another inedible meal, the meaningless grinning of the customer service representative who has no intention of serving any customer.
Within the context of manners, smiling is often the armour of genial politeness we put on to see us through all sorts of social situations. As such, we could be accused of insincerity but we insist that smiling is better, kinder, more attractive than the panoply of frowns, puzzlement, and boredom that might otherwise be the case. Remember that smiles are infectious - and spreading a little infectious happiness can only be a good thing.
Be discerning; don't be surly at home, then go out in the street and waste your smiles on total strangers. And remember that, in reserved Britain at least, indiscriminate smiles may be met with some suspicion. While some strangers will react positively to the warmth of your expression, others will wonder if there is another meaning - an imminent, and unwanted, request for something or, even more alarmingly, a sexual come-on.
Beware also of the fixed grin - it seems to presages anything other than happiness and may be interpreted negatively as insincere. To avoid the fixed grins forever immortalised in a million photo albums, don't ever say 'Cheese!'. Instead get your subjects to do what Cecil Beaton told his pals to do just before taking group photographs: enunciate 'Lesbian!' for the full range of flattering mouth configurations . . .