Often used by bodybuilders and kickboxers alike, the question posed indicates that the person in question is requesting that another person, "train" with them. It also suggests that should the other person decline the invitation then there must be a reason, illness, mental or physical as to why they should not accept.
Person 1: I no longer have a gym partner.
Person 2: "Cum train wiv me WOZ WRONG WIIIA?" -> WWWY?
What (are) you on about? When are large alpha male notices his female companion conversing with another male, the former will often stride over and bellow "WHAT YOU ON ABOUT?" repeatedly at the top of his voice, until the other males retreat.
Female: "Good afternoon kind sir..."
Male 1: "Good afternoon madam..."
Alpha Male: "WHAT YOU ON ABOUT? WHAT YOU ON ABOUT? WHAT YOU ON ABOUT?" WYOA?