Monoper

An anus. Short for 'plopper monoper'. Coined from an additional nonsense rhyme attached to the word 'plopper' due to the sound made by the contents of an anus upon toiletry impact.

Jon: "I went on a date last night"
Tim: "Did you get lucky?"
Jon: "Yeah, I put it right in the monoper."
Tim: "Up to the hairy hilt?"
Jon: "Indeed."