Chi-town Shitter Shake
After tapering your four fingers to a point (tuck your index finger under your middle finger and your pinky finger under your ring finger), insert the four into the butt while sticking your thumb into the pussy. Proceed by making a "hand-shake" motion. Similar to a shocker but with more volume and power. 
The bitch wouldn't let me do her in the butt so I gave her the ole Chi-town shitter shake... her ass was never the same again.