When you get a solid fart brewed up, fart into your cupped hand and throw it into your friend's face.
While performing said action, exclaim "Ninja, vanish!!!" in a loud, possibly Asian accented voice. While your victim is blinded by your noxious gift to the face, get the hell out of there like a ninja.
As I got up from the couch, I managed to corral a solid fart into my hand and Ninja Vanish Darla, escaping before she realized what had hit her.