How do you say hi?

Answer 1

The way you have asked is quite informal and could be considered rude in some circles.

"Hello, Sir", would be much better

Answer 2

You can say "Hi" as a simple and casual greeting to welcome or acknowledge someone. Alternatively, you could use other greetings like "Hello," "Hey," or "Good morning/afternoon/evening" depending on the time of day and formality of the interaction.