A slangier way of saying “hello” would be ossu. Like its English counterpart “what’s up,” ossu has an infinite number of variations. Ossu was originally an incredibly formal word, the kind of thing that a soldier would say to a drill sergeant—like: “SIR YES SIR!” But in a slang context, ossu comes across as a silly way to say “hi.” Here’s how two friends might greet each other, for example:
Whattup! (greeting)
ossu
‘Sup. (response)
ussu
or
Whazzap! (greeting)
uissū
Whazzaaaaaaap!!! (response)
ussussu
Good morning / Good evening
ohayō / kombanwa
There are also informal variations on “good morning” and “good evening”:
Good morning, Sunshine!
ohhā
G’morning!
ohayōn
Evenin’
konbancha
Long time no see
ohisashiburi
As in English, the next part of a greeting usually involves inquiring about the other person’s well-being.
Long time no see!
ohisa
How’s it hanging?
chōshi dōyo?
It’s hanging.
bochibochi denna
How you been?
ogenko?
Same as always, man.
ai kawarazu dayo
And just as fat as always.
ai kawarazu debu dashi
And you’re just as retarded as always.
omae wa ai kawarazu aho dashi
Yo, guys!
yō omaera
Hey.
yā
It’s been a while.
hisa bisa dana
What’s the word?
saikin dōyo?
Same old bullshit.
dōmokōmo nēyo