Results from anal penetration (see SIIMA) where the encroaching object (often the penis) has proven to be too colossol for the given anus.
Conversely, the anus may just be inadequate; this matter is subjective.
Can also result from uncommon excretory patterns if the given anus cannot withstand the extensive girth/width of the excrement.
Originates from "split anus" despite new developments suggesting that "splattered anus" would be more appropriate.
Again one must use one's discretion.
Jim: "Serious?? How'd it go?"
Bob: "Was a bit awkward.. i gave her a splanus"
Luke: "Had a mare on the shitter yesterday mate"
Dan: "what was it too sloppy?"
Luke: " the opposite! It was MASSIVE, i've got a fucking splanus!"