Sandra,

I had forgotten that reference in the song: "lost all me tin". Thanks.

And thanks to everyone else, too, especially Bob with the dictionary reference.   

But I still don't get why you would have a tin bum, of all things, if you were lucky. Little Robyn, maybe you are right, but then the term tin-backed doesn't make sense.

Tinny = also a beer can, at least here in Newcastle, NSW, Oz
Tinny = also a small aluminium boat usually with an outboard motor, or even a rowboat

John/Giok, they're probably going to be called something other than a slab in the next few years because a lot of cartons of beer are being packaged into user friendly cube-shaped boxes with a carry handle. Or maybe that's only the girlie beers, like light beer.

So, why a tin bum?

Helen