My Saigon girlfriend on xin chào: 'same same, sound like tourist"
I asked her to check a table of greetings on our site — five phrases, and I wanted to know whether Saigon people actually say them or whether they were just grammatically correct.
She confirmed them. Then she added, unprompted:
"English just say hello, say xin chào." Then she said "same same, sound like tourist". Then she added a couple more examples.
She sorted them for me in about thirty seconds:
Younger than you → chào em
A man around uncle age → chào chú
A woman around auntie age → chào cô
An elderly man → chào ông
An elderly woman → chào bà
Older man, close to your age → chào anh
Older woman, close to your age → chào chị
Seven ways to say one English word. Pick wrong and you'll still be understood. My experience is they'll correct you to help you because they know you're trying to get it right.
If you only have a week or two in Vietnam without a lot of learning time, it's ok to use xin chào, but those relationship words will come in very handy to know and are words you'll hear over and over in conversations.
What I keep learning building our site: grammatically valid and things-people-say are two different sets, and only one of them is in a grammar book.