a kangaroo loose in the top paddock

An indication of craziness, eccentricity, or foolishness. Primarily heard in Australia. Tommy must have a kangaroo loose in the top paddock if he thinks he can convince our mother to let him get a tattoo for his birthday. There's an old lady who stands on the corner yelling at strangers all day. I think there might be a kangaroo loose in the top paddock, if you catch my drift. He says he's going to start a business selling bees as pets—I think he may have a kangaroo loose in the top paddock.