To pull your ballsack out of your fly and then zip to a suitable point as to which the sack becomes taut; the balls assuming the shape of the two sides of the brain whilst veins serve to add to the realism of the shape.
The ultimate purpose of such a maneuver being to offend when engaging in light conversation with others, subsequently enjoying the outrage when they discover the brain, whilst throughout experiencing the gentle caress of a light breeze on the sack.
Essentially a ball walk
but requiring more art to pull off effectively and comfortably yet yielding a much more comical and appropriate name.
Jonny enjoyed walking the brain on a spring day, he was surprised just how long it took some people to notice his nuts were out during his strolls.