Very simply put, 'up your
bum' is the ultimate Australian
toast. It's not meant literally ('stick it up your ass and rotate', more the opposite, much like the
toast: "mud in your eye". Also, it is very important to say it the right way. If you go in 'half assed' with this
toast, you'll get strange looks (as an American friend of mine found out, when I recommended him to try it Queensland). Say it with a little confidence and a smile, but don't be aggressive - that's not the right way to go about things in the broad brown land of oz. Most of all - enjoy this toast with a large,
cold sparkling amber beverage under the Aussie sky with a good mate.
(At the pub)
Andy: Cheers big ears!
Toddles: Up your
bum!
(both take a very hefty swig, exhale loudly and exude a
happiness unknown to those not sitting with you at that moment ;-)