I just remember at school I was taught by someone ( i cannot exactly remember as it was used by missionary or teacher) three magic words.
He said if you use 3 magic words then you won't have problem with anyone around.
Please, thank you and sorry
1) Please - always use this word before asking for anything to anyone.
2) Thank you - if you receive a favour i.e. any sort of favour use thank you.
3) Sorry - if you do any kind of mistake do use the word sorry.
I realized that there may be certain words (infact sentences) which you should never use (as opposite to magic words - may be called a killer sentences and doesn't sound great)
"color of the skin"
"particular religion is better"
"kill or hurt someone"
"i or my brand is superior / better than everyone"
"calling someone with badwords like dog, bitch, color of skin, race etc"
"making fun of someone with the intension of hurting"
and list goes on..