From the main menu, go to “Options”, then “Cheats”, then “Enter Cheat”. Then play the following notes, you must strum every note/chord.
(G=Green, R=Red, Y=Yellow, B=Blue, O=Orange)

Code
Effect

(BY) (GY) (GY) (RB) (RB) (RY) (RY) (BY) (GY) (GY) (RB) (RB) (RY) (RY) (GY) (GY) (RY) (RY)
Air guitar

(GR) (GR) (GR) (GB) (GB) (GB) (RB) R [...]