An expression used when the absolute most terrible thing has happened to someone and the realization that you or anybody else cant do a damned thing about it.
You ask a guy to help you with your car because its having problems. He gets in the car after fixing it and takes off with your wallet, phone, and laptop inside. You yell for help, but soon realize that there is no one around. So the only thing to do is silently utter to yourself, Wellfuck.