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.
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?