preceeding the shocker, spocker, and show stopper, it is the first step towards a loose vag and anus. The rocker takes the index finger and places it in the vaag. It also puts the pinky finger in the anus simultaneously. This creates the devil horns hand signal, which is quite often associated with rock and roll; hence, the rocker.
"we had the tunes blastin so i just had to go rocker on her."
"he started out with the rocker, but we worked our way up to the show stopper"
"the jonas brothers love when i go rocker on their vaginas. they're too frail for the cocker."