chay is like chill, it can be used to mean chill, but it can also mean chill where in context chill does not make sense. It also means anything having to do with semen or other male sexual activities.
Ya that dude was pretty chay back there
Im going to chay all over your hair and it will take weeks to get all my chay out
Australian slang for "choice", which, in itself is used in Australian slang to describe how cool a person, act or situation is.
Can also be used as a greeting or in a demeaning or sarcastic context, usually to describe a try-hard.
Izole! You see that guy? That backflip he did was pretty chay!
Man, I can't believe the air I got off that jump! That was pretty chay!
Aw, chay! Long time no see! What are you doin' all the way out Yarrabah way?