Actually, I don't feel that total sincerity is essential in public situations. You may not care two hoots whether someone excuses you or not, but if you inadvertantly bump into them for example, you automatically say "Excuse me" because it's the accepted, socially-required custom. If you are writing a thank-you note, you may in fact have loathed the gift, but one still (in theory!) courteously thanks the giver because that's how our social system works. (Or did!) These small polite ways are the oil which keeps human contact running smoothly. Without them, people become abrasive and edgy. We live IN society and therefore we should abide by the expected and customary manners. Folk now seem to be terribly fraught and aggressive; I wonder if a return to polite good manners might defuse some of this pent-up anger and tension?