The Shaka is re-slanging the term, "The Shocker." It is when the two first fingers are placed in the vagina, while the pinky finger is placed in the anus. The ring finger is tucked away during this process.
Obviously, the term was coined because the broad gets shocked when she catches one in the butt as well as the vag.
"So I pulled off her undie wundies and put two in the pink, and one in the stink.."
"Oh damn!! you gave her the shocker?!"
"Hellz yeah brotha, hellz yeah."