What are some unwritten social rules that everyone should know?

There are rules which are not written anywhere still there are some social rules that everyone should know about. Check few of them below:

• If someone buys you a drink, buy one back – people notice.
• If you have enough money to eat out, you have enough money to tip.
• Treat the cleaner with the same respect as the CEO. Nobody will be impressed to see that how rudely you can treat someone below you but people will definitely notice if you treat them with respect.
• As a guy, to acknowledge someone you don’t know you nod down, to acknowledge someone you do know nod up. No idea why this happens but it’s true.
• If on a date or out with friends. Never leave your phone on the table face up, it subconsciously hints that your phone is more important than their company. Put it in airplane mode and in your bag/pocket.
• When you first walk into a bar/club/party, mirror the mood of others. If people are being loud you can be loud, if not don’t.
• If you have a choice between two queues, choose the one without any children or elderly people.
• When someone uses your full name, you’re probably in trouble.
• If you’re making tea/buying a drink at a pub, ask the people you’re sitting with if they want one.
• When someone tells you some news they are pleased about, act as excited as them even if you’re jealous/annoyed. You can be petty on your own time.
• If a colleague tells you they have a doctors appointment, don’t ask what it’s for, just say hope you’re ok. If they want to talk about it they will and you don’t put them in the uncomfortable position of having to tell you their personal illness.
• Whenever you are being taken out to dinner, keep a note of what the person paying is ordering and make sure you order something the same/less in value. If they get the salad don’t order the steak.
• When someone shows you a photo on their phone, don’t swipe left or right. You never know what’s next.
• If he/she says ‘sounds good, I’ll let you know when I’m free’ when you ask to meet up and they don’t get back to you, don’t push them. They probably don’t want to meet up.
• Always give up your seat for the elderly/try to help where possible. But don’t be patronizing and if you’re not sure if they’re old enough, play it safe and don’t offer. You might insult them.
• If you’re getting a long flight or train, shower before. The person next to you will appreciate it
• Starting an email using just someone’s first name with no hi, etc, immediately makes it look aggressive.
• Don’t invite someone to a meeting if they only need to be there for the last 5 minutes, invite them to the last 5 minutes or do it via email.
• If someone has headphones on, leave them alone. By the same token, realize how it looks if you put your headphones on when sitting next to someone.
• Never ask a shy person what’s wrong or ask them ‘why aren’t you talking more?’ It only makes them feel more awkward.
• Don’t tell someone they look like someone unless the person you are comparing them to is unquestionably good looking
• Don’t just ignore homeless people, say ‘no, sorry have a good day’. It is incredibly demoralizing to be ignored all day, every day and just to have someone say sorry or hi can be a welcome pick me up. You don’t need to sit down and have a long chat with them but just be polite as you would with anyone else.