See shank for root definition.
Verb: to lift up your leg or ass cheek and deliver a rousing fart at the exact same time as a loud noise, to avoid being heard, much like the lead character in The Shawshank Redemption hit the pipe with the stone during the storm.
I was at my girlfriend's house watching a movie with her parents, and I really needed to shank one, so I waited until an explosion and shawshanked it perfectly. They never heard a thing so no one knew where the smell came from.
Comes from the movie The Shawshank Redemtion, and means to break out or get away with something (out of jail, or just out of trouble)
*1* Get me the hell outta this jail cell!!!! i am so gonna go shawshank if u dont bust me out quick!
*2* You betta shawshank out of this, or he is gonna kick your ass!