There are two famous sayings "manners maketh man" and "charity begins at home" in this 21st century no one seems to have any manners. Manners can be defined as "polite behavior towards others". Old as well as young pass by the streets morning, noon and night without saying hello to each other, they both look each other in the face and walk away.
Saying "excuse, thank you, please and I’m sorry" are also difficult for many people to say. Adults interrupt conversations without saying "excuse", people bounce into others without saying "I’m sorry" and many ask for stuff without saying "please" or "thanks".
Saying "excuse" when you pass wind/gas is also not being taught. People rather say "doctor say fart free" than say "excuse" or step aside when they want to pass wind.
Even coughing in front of other persons
Long time ago children were not allowed to pass the elderly on the streets without saying good morning, afternoon or good night" otherwise they will get licks from their parents; now anything goes.
Furthermore, parents today don’t spend much, if any, time with their children teaching them what is right from wrong, teaching them the importance of manners.

"Saying Thanks" a poem taken from Alana Babb’s collection
When a customer makes a purchase
When a waitress gives good service,
When someone lends us a helping hand
We reply by saying thanks.

When someone pay us a complement
When a friend offers words of encouragement,
When someone comes and pulls us through
We say a heartfelt thank you.

Don’t forget to say thank you
It’s the least that you can do.

We have forgotten our manners and it’s about time we start to use those teachings which we have been taught by our fore parents, those manners which kept us in line, which kept us for years, after all "manners and behavior carry you through the world".
Manners also entails being nice to people, and saying "You’re Welcome" when someone thanks you.
Greeting people when you see them, looking people in the eyes when you talk to people look in their eyes. Also manners entail not interrupting other people when they are talking, sharing with others, helping other people, letting the guests go first and being on time, especially if you are meeting someone.
Another aspect of manners includes not opening a closed door until you have knocked and waited for permission to enter.
Not going into anyone else’s office, desk, box, or papers at home or anywhere else without his permission.
Not reading anyone’s mail or anything he has written (for example, a diary) unless he asks you to.
Not discussing the private affairs of your family with outsiders or tell about a family problem.
Moreover, manners also extend to the telephone, a lot of our interactions are done on the phone, and thus we need to be polite. Learn to smile on the phone through your voice. Always give the person you are calling plenty of time to get to the phone before you hang up. If someone dials your number accidentally, accept his apology. Everyone sometimes dials a wrong number. No one intends to.