derived from the term fupa (fat upper pubic or pussy area)
A fupa-knot is a fupa so large you must enter the anus or (KNOT) from a rear entry position in order to acheive sexual satisfaction.
Also describes a person who will not have intercorse with a large fupa, IE fupa not.
The girl had to take it in the anus because of her large fupa-knot.
Guy 1. Would you have sex with her?
Guy 2. Not with that huge fupa-knot.