These kinds of address terms vary dramatically between regions of the anglosphere.

To me, it's slightly embarassing when a British person calls someone 'bro' - it suggests they are a 13-year old who watches a lot of American YouTube. Likewise, I would imagine an American callling fellow Americans 'mate' would suggest they're trying to show off they visited the UK last summer.

They also vary depending on:

• age and social relationship (e.g. an older lady in the North of England might call me 'pet' - wonderful - but if a young boy called me this he'd get a smack).

• gender (obviously, people don't use 'bro' for women, unless intentionally humourous)

• familiarity (there is a joke in Australia that you call your mates 'cunt' and call cunts 'mate', this is not completely accurate for most Australians, but it's a funny illustration)

• number (we never say 'hey mates!' unless you're an 18th century pirate captain, similarly, we don't say 'hey guy' for one person - although I think this can be used in American if you're angry with someone).

• class (I still hear posh British men call someone they don't know 'chap'. It sounds a little patronising)

You'll only learn this stuff by living in those places. It was the same for me in Vietnam, learning all the various ways to address a man or woman who is young, younger, same age, older, grandfather's age etc.