When a female or male has throat cancer and gets a breathing hole in the neck. Another male penetrates that hole with his penis. The rapid penetration causes the hole to bleed while the person is trying to breath out of the hole, causing the blood to spray in the formation of a bow tie. Made famous in the movie "40 Year old Virgin".
This is the official definition from the director/co-writer, Judd Apatow.
You shit on someone's chest (or someone shits on yours) and you smush it all around with your ass cheeks, leaving a bow-tie shaped shit-smear