A cross between, or combined use of, shanking and spanking. Usually performed during or after a sexual encounter; in most cases by accident, however, some are out of anger or disappointment at a preceding exchange of sex that just occurred and left one or both participants unhappy and unsatisfied. A person may shpank their partner by spanking them with the sharp end of a knife, thus stabbing them in the butt, and leaving for an incredibly awkward and painful night. A shpank can also be performed on accident by an attempted shanking that missed, due to confusion of butt location due to saggy pants.
Ouch, my girlfriend shpanked me last night and it hurts when I sit down or poop.