Situation I
Q: If someone is talking loudly on the bus, is it a nice way to directly ask him to keep it down?
A: No. Try other means. (1) Stare at him until he realizes it and quiets down. (2) Lift your finger in a silence motion (动作) and smile. (3) Put on earphones and ignore him.
Situation II
Q: If I remember my friend's birthday a day later, should I apologize or just wish her a happy birthday like nothing happened?
A: This is the reason why the word belated was invented. "Happy belated birthday!" is short for: "Well, I know I forgot, but then I remembered. Forgive me and happy birthday."
Situation III
Q: Can I lie about seeing a text because I was too busy or lazy to respond (回复) to it?
A: Don't lie. Receiving a text does not mean you need to respond to it. Why waste a perfectly good lie when the truth will serve? "Yes," you can say if ever asked, "I saw it." No explanation is needed as to why you don't respond.