Dude

And I still use it

This is a pretty keen question

I use "Cool" quite a lot, but I don't really know if that's even considered slang any more at this point.

I still call stuff "neat".

I can't use it 'cause I'm a white boy, but I love unironic jive talk. A while back, I was watching a documentary about the black panthers and I think that was the first time I'd heard real people talking like that. Dudes were cool.

I just cannot get beyond "rad".

Gnarly

"Groovy"

It's part of my mind being rotted by Evil Dead

I'm east coast. I have a friend from California who calls all his friends "homies." It is perhaps his most endearing quality.

"I dig it"

I'm in my 40s. At a family reunion my boomer uncle was super into my usage of "dope". I had to explain to him that this isn't cutting edge, it's 30 years old.

Yeet (is this old yet)

"Hotdog!"

Thanks Jimmy Stewart!

I still use "cool beans" Andy Samberg style
https://www.youtube.com/watch?v=TOUrLn1FFCA