The three most important things a person should say is; "please", "thank you" and "excuse me".
I love to hold doors open for other people, at the gas station, stores, offices, etc. I do it not only to be courteous but I enjoy the smiles and thanks I receive.
Every now and then I run into a person such as myself and we have a polite battle over who gets to hold the door open with a lot of gesturing and words exchanged like; " after you", " no you first" , " no no go ahead".
David