Whilst performing sexual intercourse, in the Doggie Style position, the non-receiving partner lubes up his/her hand and rabbit punches the receiving partner's anus. With luck, the fist will slide in, and be rapidly retracted, causing the receiving partner to gape. The non-receiving partner then quickly spins 180 degrees, and takes a rotten dump into the receiving partner's rectum.
Amanda: "Wow Jim that feels wonderful!"
Jim: "Backfill, bitch!"
Amanda: "OH MY ASS WHY!?"