To chill or relax. Usually used by the broiest of bros or complete fucking idiots. Usually the later but in rare (and extremely awesome cases) the former.
Bro Número Uno: "Yo brah. what are you up to, my ninja?!"
Bro Número Dos: "Not too much Broseph Stalin. I'm just chayin."
Bro Número Uno: "Ohh shizam bro beans. we should meet up and chay! Maybe grab a Steve Brewschemi or two while we're at it!"
Bro Número Dos: "Fuck yeah Jay Bromeester! That'd be trill as all hell son!"