Top definition
When a girl wears really tight trousers or jogging bottoms that ride up the crack of their ass. Women of a larger frame are more likely to be visited by the Bum Monster. In extreme cases the whole of the garment can be sucked up into the body.
My god check out that fat birds ass

Yeah she's been visited by the Bum Monster
by Thrillhou123 May 17, 2009
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