blot a bum hole
This is when you have that pre-shit feeling of having a damp bum hole... To 'blot a bumhole' is when you don't actually need the shit (yet), but do need to address the dampness of the said bum hole with a kitchen towlet or similar.
Frank: "Mate, I've got a damp bum hole."
John: "Here's a napkin... go blot a bum hole."
John: "Here's a napkin... go blot a bum hole."