Derives from the German words, sheisse and geist. Literally, a shit-ghost or phantom shitter. This is a person who defecates outside of a proper facilty and in public places for the sole purpose of offending an unsuspecting passerby after such incident has taken place.
"Petty Officer Brown, did you hear the Captain's chair was hit by the sheistgeist while the ship was in port? The Captain has assigned a watch team in order to apprehend this malevolent perveyor of poop."