When someone doesn't know it's actually called lip balm, they call it lip bum. Don't ask me why they do it, they just do.
Billy: Why do you wear lip bum?
by cheesefanatic July 3, 2017
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Lips pursed in such a way that they resemble an anus.
"Don't kiss me with those silly bum lips, give me some tongue you penny-farthing driving fuckarse."
by j-oshua October 15, 2009
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The rim of your anus typically with a circumference 2πr, r being the radius of the ass pussy. This has an exponential growth whether you are excreting waste, or receiving sweet love which is proportionate to each persons bum cheek volume.
Jonathan dropped the soap and felt the exponential growth of his bum lips
by KinkyCactus April 22, 2016
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