While "hello boy" in English might be used casually among friends, in Brazil, it would be considered inappropriate and potentially offensive to address someone as "boy," even if it's meant in a friendly way.
Here are some more appropriate ways to greet a boy in Brazil:
Formal:
* Olá, garoto! (Hello, boy!) - This is still informal but less offensive than "boy" alone.
* Bom dia/Boa tarde/Boa noite, jovem! (Good morning/Good afternoon/Good evening, young man!) - This is a polite and respectful way to greet a boy.
Informal:
* E aí, cara! (Hey, dude!) - This is a common, friendly greeting among friends.
* Oi! (Hi!) - This is a very casual greeting.
Important Note: The best greeting depends on the context and your relationship with the person you are addressing. It's always best to err on the side of caution and use a more formal greeting unless you are very familiar with the person.