Something bad, or something that doesn't perform as espected.
My new phone is absolute dogwank. It's useless.
A person can get a nonce pass from noncy behaviour if the subject of the discussion is older than the person talking.
Jack: Laura is well fit. I'd deffo smash.
Matt: Mate that's kinda booky that you're talking about her like that, isn't she like 16?
Jack: Don't worry, I'm 16 too. I've got the nonce pass.
Matt: Oh okay, safe.