My male loves to have his spine kind of pinched. I don't rub it, he's not too receptive to that idea, however, if you put your fingers on both sides of his "bristles" and gently close your fingers while moving your fingers upwards you may find out that he likes it. It was suggested to me by the breeder that I got my male from and Arnie closes his eyes, lifts his chin up and makes a little grunting sound. He all but falls over from how relaxed he gets.
I find it amazing how individual our chameleons are. They each have their own food preferences, handling preferences, and now this. LOL They are marvelous little beasts, aren't they.