I discovered the joy of P.R.D. (Plug Removal Denial) on my own, when I found that I could inflate my but plug so big that I couldn't expell it without letting air out of it first.
The size and pressure of an inflated but plug can give the feeling of constipation or the feeling of needing to push a baby out (depending on your perspective).
These feelings can be erotic if you or someone denies you from letting some air out of the but plug. Some childbirth fetish people may like this in the vagina and even rectum.
If another person is involved in this type of play, a safeword should be established ahead of time.