anal sex, and the prelude to an amusing rhyme which kids at school write on each others textbooks to get their friends in trouble:
up the bum, no harm done!

additions:
with a thumb, twice as fun!
with ya mum, watch me cum!
by me old fruity September 30, 2006
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The ramming of aerodynamic and not so arodynamic objects up the hrmm... anus
Everybody goes to take michael's mum up the bum while he watches in dispair.
Then he decides to go take some tall dark and hansome man up the bum in a dark alleyway, allllll night long. Bless his little gay soul
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The action of having anal sex to ward off babies.
`meth: Great now I got SR pregnate.
Soul-Reaver: Hm? Up the bum, no babies
by Cornflake September 23, 2004
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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 ;-)
by AndrewO May 05, 2006
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