Bum butter is the acumilation of crud and smegg in the crack of your arse
Bloody hell my pants smell of bum butter
by Hooligansteve August 23, 2006
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The butter like substance you find between the sweaty crack of someones behind.
My new girlfriend is really hot, it's too bad about her serious bum butter problem.
by Monamourski March 2, 2008
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To experience a stroke of good fortune. British.
Saw Mark down the market, he found a finger in a can of tomatoes and got a huge settlement.

So he's got his bum in the butter, again.
by Shuaman October 24, 2018
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