When you see your neighbor. *We don't greet our neighbors with Otsukaresamadesu.
When we greet someone in the afternoon, we say:
Konnichiwa
However, we usually don't use Konnichiwa with our family or close friends.
So think Konnichiwa is the equivalent of "Good afternoon." You don't say "good afternoon" to your family or close frineds, right?
It's the same in Japanese.
Actually, there isn’t a specific phrase for casually greeting friends in Japanese like "hi", "hey", or even "hello".
Some people might say:
Oh
Yoh
Yahho
but it really depends on the person and the context.
Personally, I don't use any of those greetings, except when I see my sister-in-law.
I greet her with Yahho because that's how she greets me. But none of my friends greet me like that.
But there is one greeting that's commonly used among friends, which is:
Otsukare
We usually say it when leaving the office to show appreciation for our coworkers' hard work like "good job".
But we also use it when we meet friends, even though it doesn't really mean "good job" in that context.
Most people don't even know why we say it, but it's a common way to greet each other especially after we enter university.
You can also use it when you send a message to your friend. So when I usually send a message to my friend, I say Otsukare first.
So if you want to greet your Japanese friends in a casual way, you can try saying Otsukare.
By the way, the Keigo version is:
OtsukareSamadesu
When you see your friend.
When you greet your teacher. *We don't greet our teacher with Otsukaresamadesu.
Greetings between senpai and kōhai. You can also say Otsukare/Otsukaresamadesu.
When you greet your coworkers. It's common to greet coworkers with Otsukare or Otsukaresamadesu and not Konnichiwa.
When you greet your boss.
How to say "Hello" in Japanese can be a bit complicated, and there's no one-size-fits-all answer for casual greetings.
As a general rule, stick with Konnichiwa when you're greeting someone you're not very close to.
For those you are close with, particularly if you usually speak in Tameguchi , Otsukare is a common option, or just pay attention to how they greet you, and you can mirror that — like I do with my sister-in-law with Yahhō.
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When we say "hello" on the phone, we say Moshi moshi, and never Konnichiwa.